green buildings

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UNIT 2
B) Water conservation and efficiency
i)Rainwater harvesting methods for roof & non-roof
ii)Reducing landscape water demand by proper irrigation system
iii)Water efficient plumbing system
iv) Water metering
v)Waste water treatment
vi)Recycle and reuse systems
i)Rainwater harvesting methods for roof&non-roof
Broadly there are two ways of harvesting rainwater
1. Surface runoff harvesting
2. Roof top rainwater harvesting
Surface runoff harvesting
In urban area rainwater flows away as surface runoff. This runoff could be caught and used
for recharging aquifers by adopting appropriate methods. The rain water that is collected
from the open areas may be diverted by drain pipes to a recharge dug well / bore well through
filter tanks. The abandoned bore well/dug well can be used cost effectively for this purpose.
Methods of recharging subsurface aquifers
The various methods of recharging subsurface aquifers are:
1. Through recharge pit.
2. Recharge through abandoned hand pump.
3. Recharge through abandoned dug well/open well.
4. Through recharge trench.
5. Recharge through shaft.
6. Recharge trench with bore.
Through recharge pit This method is suitable where permeable strata is available at shallow
depth. It is adopted for buildings having roof area up to 100 sqm. Recharge pit of any shape is
constructed generally 1-2 m wide and 2-3 m deep. The pit is filled with boulders, gravel and
sand for filtration of rain water. Water entering in to RWH structure should be silt free. Top
layer of sand of filter should be cleaned periodically for better ingression of rain water in to
the sub soil.
Recharge through abandoned hand pump In this method, an abandoned hand pump is
used as recharging structure. It is suitable for building having roof top area up to 150 sqm .

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Roof top rain water is fed to the hand pump through 100 mm dia. pipe. Water fed in the Rain
water harvesting structure should be silt free. Water from first rain should be diverted to drain
through suitable arrangement. If water is not clear then filter should be provided.
Recharge through abandoned dug well / open well In this method, a dry / unused dug well
can be used as a recharge structure. It is suitable for buildings having a roof top area more
than 100 sqm . Recharge water is guided through a pipe of 100 mm to the bottom of the well.
Well cleaning and desilting is imperative before using it. Recharge water guided should be
silt free, otherwise filter should be provided. Well should be cleaned periodically and
chlorinated to control bacteriological contamination.
Through recharge trench This method is used where permeable strata is available at
shallow depth. It is suitable for buildings having roof top area between 200 & 300 sqm. In
this method, trench of 0.5-1.0 m wide, 1-1.5 m deep and of adequate length depending upon
roof top area and soil/subsoil characteristics should be constructed and filled with boulders,
gravel and sand. Cleaning of filter media should be done periodically.
Recharge through shafts This method is suitable where shallow aquifer is located below
clayey surface. It is used for buildings having roof top area between 2000 &5000 sqm.
Recharge shaft of diameter 0.5-3 m and 10-15 m deep is excavated mechanically. The shaft
should end in impermeable strata. The shaft should be filled with boulders, gravel and sand
for filtration of recharge water. Top sand layer should be cleaned periodically. Recharge shaft
should be constructed 10-15 m away from the buildings for the safety of the buildings.
Recharge trench with bore This method is used where sub-soil is impervious and large
quantity of roof water/ surface run off is available. In this, trench is made 1.5-3 m wide and
10-30 m length depending upon water availability. Wells of 150-300 mm dia. and 3-5 m deep
(below pervious layer) are constructed in the trench. Numbers of wells to be dug are decided
in accordance to water availability and rate of ingression. Trench is filled with filtration
media. A suitable silt chamber is also inserted with grating for water diverting arrangements.
Roof top rainwater harvesting
Rainwater harvesting refers to structures like homes or schools, which catch rainwater and
store it in underground or above-ground tanks for later use. One way to collect water is
rooftop rainwater harvesting, where any suitable roof surface — tiles, metal sheets, plastics,
but not grass or palm leaf — can be used to intercept the flow of rainwater in combination

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with gutters and downpipes (made from wood, bamboo, galvanized iron, or PVC) to provide
a household with high-quality drinking water
Rooftop Rain Water Harvesting is the technique through which rain water is captured
from the roof catchments and stored in reservoirs. Harvested rain water can be stored in
sub-surface ground water reservoir by adopting artificial recharge techniques to meet the
household needs through storage in tanks.
The Main Objective of rooftop rain water harvesting is to make water available for future
use. Capturing and storing rain water for use is particularly important in dryland, hilly, urban
and coastal areas. In alluvial areas energy saving for 1m. rise in ground water level is around
0.40 kilo watt per hour.
Need for Rooftop Rain Water Harvesting
1. To meet the ever increasing demand for water
2. To reduce the runoff which chokes storm drains
3. To avoid flooding of roads
4. To augment the ground water storage and control decline of water levels
5. To reduce ground water pollution
6. To improve the quality of ground water
7. To reduce the soil erosion
8. To supplement domestic water requirement during summer, drought etc.
Advantages of Rain Water Harvesting
1. Provides self-sufficiency to your water supply
2. Reduces the cost for pumping of ground water
3. Provides high quality water, soft and low in minerals
4. Improves the quality of ground water through dilution when recharged to ground water
5. Reduces soil erosion in urban areas
6. The rooftop rain water harvesting is less expensive
7. Rainwater harvesting systems are simple which can be adopted by individuals
8. Rooftop rain water harvesting systems are easy to construct, operate and maintain
9. In hilly terrains, rain water harvesting is preferred
10. In saline or coastal areas, rain water provides good quality water and when recharged to
ground water, it reduces salinity and also helps in maintaining balance between the fresh-
saline water interface

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11. In Islands, due to limited extent of fresh water aquifers, rain water harvesting is the most
preferred source of water for domestic use
12. In desert, where rain fall is low, rain water harvesting has been providing relief to people
Safety Consideration Storage in Ground Water Reservoir
1. For rooftop rain water harvesting through existing tubewells and handpumps, filter or
desilting pit should be provided so that the wells are not silted.
2. Such tubewells if pumped intermittently, increase the efficiency of recharge.
3. If the ground water reservoir is recharged through, shaft, dug well etc., inverted filter may
be provided.
Storage in Tanks
1. A storage tank should not be located close to a source of contamination, such as a septic
tank etc.
2. A storage tank must be located on a lower level than the roof to ensure that it fills
completely.
3. A rainwater system must include installation of an overflow pipe which empties into a
non-flooding area. Excess water may also be used for recharging the aquifer through dug well
or abandoned handpump or tubewell etc.
4. A speed breaker plate must be provided below inlet pipe in the filter so as not to disturb the
filtering material.
5. Storage tanks should be accessible for cleaning.
6. The inlet into the Storage tank should be screened in such way that these can be cleaned
regularly.
7. Water may be disinfected regularly before using for drinking purpose by chlorination or
boiling etc.
How Much You Can Collect Collection Efficiency How efficiently the rainfall can be
collected depends on several considerations. Collection efficiencies of 80% are often used
depending on the specific design.
Rainfall Reliability. The first step is to determine how much water would be generated from
your roof area. Average monsoon rainfall is used for this purpose.
Formula: Total quantity of water to be collected (cu.m.) = Roof Top Area (Sq.m.) x Average
Monsoon Rainfall (m) x 0.8
All designs of RWH systems basically include: (A) rain, (B) catchment area (roof, pavement
area, storm drains etc.), (C) conveyance system (gutters, down pipes), (D) storage units or
tanks (over ground / underground) and (E) distribution system (pipelines, pumps). In

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addition, there are some complementary units like filter/screens, first-flush diverters,
disinfection methods (chlorination, boiling, UV) and overflow management pipes to complete
the RWH system.
The “Rational Method” states that Potential Rainwater Harvested = Rainfall (mm/year) x
Catchment area (m2) x Runoff Coefficient;
run-off coefficient is defined as amount of water that runs-off the catchment area and can be
collected relative to the amount of rainwater that it actually receives. It differs case-wise
depending on surface of the catchment area. Keeping in mind the above, some construction
guidelines are: (1) Catchment Area: use of paints, heavy metals, tiles for coating should be
conscientious; (2) Gutters PVC or G.I: non-corrosive & sturdy, width of the gutters based on
catchment area; (3) Filters/Screens: coarse mesh (5 mm) or fine mesh (0.4 mm); first-line
defenceto protect water quality; (4) Storage tanks (RCC, ferrocement, plastic, etc.): size
depends on many factors like amount of rainfall, no. of end users, cost etc.
ii)Reducing landscape water demand by proper irrigation system
Certain landscapes create harmony, pleasure and serenity. Some are high maintenance while
others are functional, efficient, and water saving. "Xeriscaping," a term created from the
Greek root "xeros" (for "dry") and "scape" (for "vista"), is a method of landscaping, which
helps create, harmonious yet water efficient landscapes. The basic principles of Xeriscaping
involve seven simple steps, which may assist gardeners in creating water-conserving

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landscapes. Both new and established landscapes can benefit from xeriscaping, which focuses
on:
Effective Design - It is important to plant "the right plant in the right place" and to group
plants with similar needs together. Examine and assess planting areas as to: hardiness zone,
slope (degree of steepness), exposure, (hot/sunny, cool/shady,) soil type, (heavy soil, sandy
soil, etc), good drainage, poor drainage, etc., and plan and plant accordingly. Also consider
the maintenance of the designed landscape as to whether it will require frequent mowing,
fertilizers, pesticide application, pruning, etc. High frequency watering translates into high
maintenance, potential high cost and overuse of a limited resource.
Soil Improvement - In some planting areas, the addition of soil amendments such as
compost, rotted leaves or manure, etc. may improve soil structure and increase the water
holding capacity of the soil.
Turf Areas - Use of drought tolerant grasses will aid in water conservation. Also, avoid
narrow, isolated strips of turf. Not only is maintenance more costly but watering may be
difficult, sometimes wasteful. Maintaining a lush, green lawn during a drought, usually
means frequent watering. To conserve water during drought, allow turf to go dormant. If
dormant turf is unacceptable, turf could be reduced to particular areas of importance.
Expanded Use of Mulches - Organic mulches reduce water evaporation from the soil,
suppress weeds that may compete with desirable plants for available moisture, and moderate
soil temperature. Mulch should be placed over the root zones of plants and never mounded or
placed against the stems or trunks. In some instances, mulched planting beds planted with
drought tolerant plants may be a desirable replacement for turf areas.
Efficient Irrigation - In many cases, well-planned sprinkler systems can save water. For
efficient water use, plan to irrigate turf areas separately from other plantings. Also landscape
plantings should be grouped according to similar water needs. Turf areas are best watered
with sprinklers. Trees, shrubs, garden flowers, and ground covers can be watered efficiently
with low volume drip, spray, or bubbler emitters. Regular adjustment of irrigation systems
will save water and money. Make sure the irrigation system is designed to fit the needs of the
landscape, the water needs of the plants and zoned to reduce unnecessary applications of
water. Automatic irrigation systems have the potential to waste water and should be adjusted
according to soil moisture and plant need.
Appropriate Maintenance - Regular maintenance (weeding, pruning, etc.) preserves the
intended beauty of a landscape and may save water. Proper planting and appropriate and
timely maintenance will help ensure the health and longevity of plants.

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Selection of Low-Water Demand Plants - Evaluating the landscape and choosing plants
that usually have lower water needs and also have fewer insect and disease problems can
result in an attractive landscape that conserves water, reduces labor and pesticide usage, and
produces an interesting and attractive landscape. When selecting drought tolerant plants for a
landscape, it is important to remember that plants do need water to become established.
Water-efficient Landscape Irrigation Methods
With common watering practices, a large portion of the water applied to lawns and gardens is
not absorbed by the plants. It is lost through evaporation, runoff, or being pushed beyond the
root zone because it is applied too quickly or in excess of the plants’ needs. The goal of
efficient irrigation is to reduce these losses by applying only as much water as is needed to
keep your plants healthy. This goal is applicable whether you have a Xeriscape or a
conventional landscape.
To promote the strong root growth that supports a plant during drought, water deeply and
only when the plant needs water. For clay soils, watering less deeply and more often is
recommended. Irrigating with consideration to soil type, the condition of your plants, the
season, and weather conditions—rather than on a fixed schedule—significantly increases
your watering efficiency. Grouping plants according to similar water needs also makes
watering easier and more efficient.
Irrigating lawns, gardens, and landscapes can be accomplished either manually or with an
automatic irrigation system. Manual watering with a hand-held hose tends to be the most
water-efficient method. According to the AWWA Research Foundation’s outdoor end use
study, households that manually water with a hose typically use 33 percent less water
outdoors than the average household. The study also showed that households with in-ground
sprinkler systems used 35 percent more water, those with automatic timers used 47 percent
more water, and those with drip irrigation systems used 16 percent more water than
households without these types of systems. These results show that in-ground sprinkler and
drip irrigation systems must be operated properly to be water efficient.
You can use a hand-held hose or a sprinkler for manual irrigation. To reduce water losses
from evaporation and wind, avoid sprinklers that produce a fine mist or spray high into the
air. Soaker hoses can also be very efficient and effective when used properly. Use a hand-
held soil moisture probe to determine when irrigation is needed.
To make automatic irrigation systems more efficient, install system controllers such as rain
sensors that prevent sprinkler systems from turning on during and immediately after rainfall,

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or soil moisture sensors that activate sprinklers only when soil moisture levels drop below
preprogrammed levels. You can also use a weather driven programming system. Drip-type
irrigation systems are considered the most efficient of the automated irrigation methods
because they deliver water directly to the plants’ roots. It is also important to revise your
watering schedule as the seasons change. Over-watering is most common during the fall
when summer irrigation schedules have not been adjusted to the cooler temperatures.
iii)Water efficient plumbing system
Plumbing systems are complex, expensive, and largely inaccessible when construction is
complete. For those reasons, careful planning pays big dividends. There are two sides to
every residential plumbing system: supply and waste. Within those broad categories are a
number of subsystems, many of which present opportunities for conserving water, energy, or
both. A well designed plumbing system is capable of saving thousands of gallons of water
every year. In many communities, saving water also saves energy because a lot of electricity
is used to pump water from source to houses.
5 Water-Saving Green Plumbing Fixtures
Pressure Reducing Valves. A good pressure reducing valve will reduce the strain on your
pipes and help water flow easier in your home. ...
Low-Flow Shower Heads. Taking a shower is inherently efficient when compared to taking
a bath. ...
Low-Flush Toilets. ...
Recirculating Hot Water Pumps. ...
Efficiency Faucets.
What actually is green plumbing? It is an environmentally friendly and cost efficient
plumbing service. By adopting green plumbing, you will reduce waste water, recycle used
water and use eco-friendly and sustainable materials. Another aspect of green plumbing is the
use of solar and wind power as alternate sources of energy to provide water.
Green Plumbing Materials and Solutions: The green plumbing materials are often
polymer-based. Traditionally, pipes and water fixtures were made out brass and metal alloys.
They eventually need replacement as they corrode over time. It’s not only the corrosion that

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causes a problem, but also the corroded material finds its way into the water, contaminating it
and as a result affecting the health of people.
Water pipes: Good water pipes mean no water leaks which means less waste. The proper
piping material is also able to handle differing water pressures. For example, a cross-linked-
polyethylene-pipe (PEX) used with steel is the best option for maintaining the correct
temperature of water passing through. This material, PEX, is also more flexible meaning it
can accommodate water pressure changes. The pipes can also be insulated to reduce heat loss
during winter. That’s another cost saving there.
Toilets: Check out the better designed toilets that lower your water consumption. An
environmentally-friendly toilet is designed to use less water than regular toilets. The water
savings from this alone can be as high as 60%.
Taps: You must have taps to deliver water into the house, be it the kitchen or the bathroom.
Taps are one of the main culprits for water wastage. Eco-friendly taps are available that have
a lower pressure delivery system which helps reduce water wastage. Less water wasted
means lower costs in both utilities and ultimately decreased energy costs. While better
designed taps will certainly help, turning taps off to stop unnecessary water use is going to be
great help as well.
Showers: Not all the water that flows from your showerhead is used. A better
designed showerhead as a green plumbing option will provide better functionality. You can
save an additional 25% by using technology that provides a lower flow rate. You still get wet
in the shower, but with less water you save energy and costs.
Garden Irrigation: We all love our gardens in Australia, hence the proliferation of an
outdoor watering system. No water means plants die, especially in Australian summer during
which the heat is relentless. The problem with outdoor reticulation is that it is one of the main
causes of water wastage in a household. Newer control technologies are available through
green plumbing that deliver the right amount of water at the right time of day. Watering
schedules can be entered into the computerised system to ensure that you garden grows and
flourishes. Another aspect of reticulation is the positioning set up of the sprinkler heads.
Water metering
Water metering is the process of measuring water use. Water meters are used to measure the
volume of water used by residential and commercial buildings that are supplied with water by
a public water supply system. Water meters can also be used at the water source, well, or

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throughout a water system to determine flow through a particular portion of the system.
There are several types of water meters in common use. The choice depends on the flow
measurement method, the type of end-user, the required flow rates, and accuracy
requirements.
Types of metering devices
There are two common approaches to flow measurement, displacement and velocity, each
making use of a variety of technologies. Common displacement designs include oscillating
piston and nutating disc meters. Velocity-based designs include single- and multi-jet meters
and turbine meters.
There are also non-mechanical designs, for example, electromagnetic and ultrasonic meters,
and meters designed for special uses. Most meters in a typical water distribution system are
designed to measure cold potable water only. Specialty hot water meters are designed with
materials that can withstand higher temperatures. Meters for reclaimed water have special
lavender register covers to signify that the water should not be used for drinking.
Additionally, there are electromechanical meters, like prepaid water meters and automatic
meter reading meters. The latter integrates an electronic measurement component and
a LCD with a mechanical water meter. Mechanical water meters normally use a reed switch,
hall or photoelectric coding register as the signal output. After processing by
the microcontroller unit (MCU) in the electronic module, the data are transmitted to the LCD
or output to an information management system.
Water meters are generally owned, read and maintained by a public water provider such as a
city, rural water association or private water company. In some cases an owner of a mobile
home park, apartment complex or commercial building may be billed by a utility based on the
reading of one meter, with the costs shared among the tenants based on some sort of key (size
of flat, number of inhabitants or by separately tracking the water consumption of each unit in
what is called submetering).
Prepaid water meters
Meters can be prepaid or postpaid, depending on the payment method. Most mechanical type
water meters are of the postpaid type, as are electromagnetic and ultrasonic meters. With
prepaid water meters, the user purchases and prepays for a given amount of water from a
vending station. The amount of water credited is entered on media such as an IC or RF type
card. The main difference is whether the card needs contact with the processing part of the
prepaid water meter. In some areas, a prepaid water meter uses a keypad as the interface for
inputting the water credit.

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Waste water treatment
Wastewater treatment is a process used to
remove contaminants from wastewater or sewage and convert it into an effluent that can be
returned to the water cycle with minimum impact on the environment, or directly reused. The
latter is called water reclamation because treated wastewater can be used for other purposes.
The treatment process takes place in a wastewater treatment plant (WWTP), often referred to
as a Water Resource Recovery Facility (WRRF) or a Sewage Treatment Plant (STP).
Pollutants in municipal wastewater (households and small industries) are removed or broken
down.
The treatment of wastewater is part of the overarching field of sanitation. Sanitation also
includes the management of human waste and solid waste as well as stormwater (drainage)
management. By-products from wastewater treatment plants, such as screenings, grit
and sewage sludge may also be treated in a wastewater treatment plant.
Biological processes can be employed in the treatment of wastewater and these processes
may include, for example, aerated lagoons, activated sludge or slow sand filters. To be
effective, sewage must be conveyed to a treatment plant by appropriate pipes and
infrastructure and the process itself must be subject to regulation and controls. Some
wastewaters require different and sometimes specialized treatment methods. At the simplest
level, treatment of sewage and most wastewaters is carried out through separation
of solids from liquids, usually by sedimentation. By progressively converting dissolved
material into solids, usually a biological floc, which is then settled out, an effluent stream of
increasing purity is produced
Phase separation
Sedimentation
Solids like stones, grit and sand may be removed from wastewater
by gravity when density differences are sufficient to overcome dispersion
by turbulence. Gravity separation of solids is the primary treatment of sewage, where the unit
process is called "primary settling tanks" or "primary sedimentation tanks". It is also widely
used for the treatment of other wastewaters. Solids that are heavier than water will
accumulate at the bottom of quiescent settling basins. More complex clarifiers also have
skimmers to simultaneously remove floating grease like soap scum and solids like feathers or

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wood chips. Containers like the API oil-water separator are specifically designed to separate
non-polar liquids
Filtration
Suspended solids and colloidal suspensions of fine solids may, generally following some
form of coagulation, be removed by filtration through fine physical barriers distinguished
from coarser screens or sieves by the ability to remove particles smaller than the openings
through which the water passes. Other types of water filters remove impurities by chemical or
biological processes described below.[6]
Oxidation
Oxidation reduces the biochemical oxygen demand of wastewater, and may reduce the
toxicity of some impurities. Secondary treatment converts organic compounds into carbon
dioxide, water, and biosolids. Chemical oxidation is widely used for disinfection.
Biochemical oxidation
Secondary treatment by biochemical oxidation of dissolved and colloidal organic
compounds is widely used in sewage treatment and is applicable to some agricultural and
industrial wastewaters. Biological oxidation will preferentially remove organic compounds
useful as a food supply for the treatment ecosystem. Concentration of some less digestible
compounds may be reduced by co-metabolism. Removal efficiency is limited by the
minimum food concentration required to sustain the treatment ecosystem
Chemical oxidation
Chemical (including Electrochemical) oxidation is used to remove some persistent organic
pollutants and concentrations remaining after biochemical oxidation.[8] Disinfection by
chemical oxidation kills bacteria and microbial pathogens by adding ozone, chlorine or
hypochlorite to wastewater
Polishing
Polishing refers to treatments made following the above methods. These treatments may also
be used independently for some industrial wastewater. Chemical reduction or pH adjustment
minimizes chemical reactivity of wastewater following chemical oxidation.[9] Carbon
filtering removes remaining contaminants and impurities by chemical absorption onto
activated carbon.[2]:1138 Filtration through sand (calcium carbonate) or fabric filters is the
most common method used in municipal wastewater treatment.

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Wastewater treatment plants
Wastewater treatment plants may be distinguished by the type of wastewater to be treated, i.e.
whether it is sewage, industrial wastewater, agricultural wastewater or leachate.
Sewage treatment plants
Tertiary treatment
Industrial wastewater treatment plants
Agricultural wastewater treatment plants
Leachate treatment plants
Recycle and reuse systems
Reclaimed or recycled water (also called wastewater reuse or water reclamation) is the
process of converting wastewater into water that can be reused for other purposes. Reuse may
include irrigation of gardens and agricultural fields or replenishing surface water and
groundwater (i.e., groundwater recharge).
Wastewater reuse
On-site wastewater reuse can reduce water use in both urban and rural households. At
present, most homes use potable (drinkable) water for practically everything in the house and
garden. We are literally flushing our drinking water down the toilet!
Opportunities to reuse wastewater and regulation of its treatment vary according to where
you live. Urban households typically have a connection to a centralised, or reticulated,
sewage system, whereas rural households manage their wastewater on site.
Two types of wastewater are created in a home: greywater and blackwater.
Greywater is wastewater from non-toilet plumbing fixtures such as showers, basins and taps.
Blackwater is water that has been mixed with waste from the toilet. Because of the potential
for contamination by pathogens and grease, water from kitchens and dishwashers should be
excluded from greywater and considered as blackwater.
Each wastewater type must be treated differently and can be used in various ways. Greywater
is ideal for garden watering, with the appropriate precautions, such as using low or no sodium
and phosphorus products and applying the water below the surface. Appropriately treated
greywater can also be reused indoors for toilet flushing and clothes washing, both significant
water consumers.

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Blackwater requires biological or chemical treatment and disinfection before reuse. For single
dwellings, treated and disinfected blackwater can be used only outdoors, and often only for
subsurface irrigation. Check with your local council or state health department on local
requirements.
Advantages of reuse
By using wastewater as a resource rather than a waste product you can:
 reduce water bills
 use fewer water resources
 irrigate the garden during drought or water restrictions
 cut down the amount of pollution going into waterways
 help save money on new infrastructure for water supplies and wastewater treatment
 decrease demand on infrastructure for sewage transport, treatment and disposal,
allowing it to work better and last longer.
Disadvantages of reuse
The disadvantages of reusing wastewater also need to be considered. Currently, the main
disadvantage for most households is the financial cost of installing and maintaining a reuse
system. The attractiveness of the investment would depend on:
 the extent of centralised wastewater treatment services available
 the price of water in your area (urban) or scarcity of water (rural)
 whether you are replacing an existing system or starting from scratch
 the length of time you intend to live in your current house
 the type of system — annual operating and maintenance costs vary between systems
whether a restriction free, reliable water supply is valuable to you — wastewater reuse is
often a much more reliable secondary source of water than common rainwater tank
installations.