Building a small slow sand water filter for individual use
San Juan Sunset
images by: David Tarsi

New filter design
This is the new filter started in operation the first week in April 2008. The water that goes into this filter is not as contaminated as the roof water, but still has nasty bacteria in it. This water comes from a surface water source. There have been two tests on this filter. The first one, at about 3 weeks showed it still was allowing some coliform through. The first test and the most recent test can be found here: As of June 2 the filter is working! No coliform, no ecoli, or fecal coliform are found in the water output. This filter's container has a volume of about 65 gallons and is about 1 foot deeper than the other filter. There is about 6 inches of water on top of the sand. It gives a slighlty higher flow rate - about 4 gallons per hour. A small dc pump feeds the water into the bucket via a pressure/flow regulator. Estimated filter cost - under 100 dollars. Maintaince cost - under 10 dollars per year. Expected life of the filter if the filter is kept out of the sunlight: 10 years or more. The dc pump used can easily be powered by a small solar array with 1 deep cycle battery. I do not have time now for any more details until school is finished. Much more to come later . . . .

Sand used:
"Fine sand" called "Natural sand"
by the manufacturer Oldcastle industries.
50 lb bags.
Cover the pea gravel with 6 inches of this sand.

Also the graded sand used:
.15mm effective filtration size.

WARNING: Know exactly where the sand you use
comes from and what is in it before you ever drink
any water that has passed through it in your filter.

There are two standards used to approve materials
for use with potable water that suppliers/manufactures can
choose to use: (National Sanitation Foundation)NSF 061 and
(American Water Works Association) AWWA B100-01.

(recycled food grade plastic container 40 inches tall
22 inch diameter with large threaded lid):
91.44 cm (36 inches) of sand,
with 10.16 cm (4 inches) of water on top.
Diameter: 55.88 cm (22 inches)

Volume of sand:
224139.6 cubic centimeters (13678 cu in)

Volume of water on top:
24908 cubic centimeters (1520 cu in)

Volume of water held by sand:
112069.8 cubic centimeters (6839 cu. in.)

Total volume of water:
136962.5 cubic centimeters (8358 cu. in.)

Flow (as of April 9 2008):
with 4 inches (10.16cm) of water on top of the sand surface:
(32.44 liters) per hour
(8.57 gallons per hour or 1979.67 cu. in. per hour)
53.76 cubic centimeters per minute or .022 cm per minute
(.00864 inches per minute)

Flow (fiter had been frozen.
It was restarted as of Feb 8 2009):

with 7.9 inches (20cm) of water on top of the sand surface:
(72 liters) per hour

Flow (as of April 8 2009):
with 7.9 inches (20 cm) of water on top of the sand surface:
(42 liters) per hour

The filter is still in operation. As of March 1, 2010 the flow rate
is 24 litres per hour (6.3 gallons per hour). It has not been necessary
to clean the filter, although the flow rate has gone from about
40 litres per hour to 24 litres per hour.

PVC pipe used throughout the filter:
Schedule 20 pvc 1/2 inch unless otherwise noted;
no connections are glued.
A charcoal filter is used on the output
which uses 1 1/4 inch pvc schedule 20 pipe.
Leave one side unglued so the charcoal can be
changed. Use charcoal approved for potable water.

cubic inch = 16.387064 cubic centimeters
2.54 cm = 1 inch
1 US gallon = 3785.41178 cubic centimeters
1 US gallon = 3.78541178 liters
1 liter = 0.264172052 US gallons

(For the graded sand I would recommend using the same
size but use a sand that is designed specifically for
drinking water filters.)

new filter thumb
Larger version

new filter
Complete filter
baffle pipes
connection at the bottom of the bucket

baffle pipes
Bucket in place connected to the baffle through the top of the filter lid
baffle pipes
complete filter set up
baffle pipes
Flow regulator to fit inside bucket

baffle pipes
Baffle assemblly

baffle pipes
Clean water out

baffle pipes
Pressure regulator and vent


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