1. Roughing Filters for Rural Gravity-Fed Water Systems
in Developing Countries
Erin Paul empaul@stanford.edu Stanford University, Palo Alto
Background
• WHO standards for drinking water
require turbidity of < 5 NTU for
effective chlorination
• During the rainy season, very few
rural water systems meet that
standard and many stop
chlorinating because of the high
turbidity.
• Slow sand filters (SSF) with gravel
pre-filters have shown promise for
small towns in developing
countries, but currently are
expensive relative to the water
system cost and require more
maintenance than most villages can
provide
• Previous pilot projects of SSF
show that gravel pre-filters
effectively reduce turbidity
• Do a pilot project in the
department of El Paraiso,
Honduras.
• Communities with gravity-fed
systems will be randomly assigned
to receive filters or be part of the
control group. Build filters and
train community plumbers to clean
& maintain them
• Evaluate impact of the filters
through indicators for turbidity
during the wet and dry season,
diarrhea cases, and other water
quality indicators
Gravity Fed Water Systems Filter Design Evaluation
Justification
Parts of the water system
1.Watershed
2.Dam or spring box
3.Conduction line
4.Storage tank with hypochlorinator
5.Distribution line
6.Distribution network
7.Household tap
**Note: Systems with dams have a
sedimentation tank just after the dam
Rural water systems with only
sedimentation tanks and
hypochlorinators at the tank do not
reduce turbidity enough, resulting in
bad taste and color, and ineffective
disinfection. Millions of people drink
water from such systems.
• Water flows upward by gravity,
removing particles as it passes
through the filter media.
• To backwash, close outlet valve and
open cleanout valves. Water flows
downward carrying particles with it.
• Roughing filters will effectively
remove particulate matter to reduce
turbidity to < 5 NTU.
• A simple, reverse flow design, will
make the filters easy to build and
clean
• By using local materials, the cost
will be < $500
Hypotheses
Roughing filters would be installed
just after sedimentation tank.
Objectives
• Design a simplified filter prototype
• Do pilot project in Honduras
• Evaluate results of pilot project
• Include filters as a standard part of
gravity-fed water systems
Post Evaluation
• Create a design toolkit in English,
Spanish, and French
• Complete drawings
• Excel template to size filters for
specific villages
• Hold design and construction
workshops around the world to
promote filter
z z z
Inflow from
sedimentation
tank
Outflow to
conduction line
3 Cleanout valves
Coarse Sand
Fine Gravel
Coarse Gravel
Brick
walls
covered
with
mortar
Concrete paneled lid
Treated Water