http://www.aqsolutions.org/resources/DIY.pdf

The water filtration system described here is designed around a general set of parameters, making conservative
estimates regarding its capacity for contaminant adsorption. In place of experimental data using specific
agrichemical pesticides, we regard dissolved organic carbon (DOC) as our general contaminant and design the
system around its removal. Several studies have shown that DOC adsorption by granular carbon can block or
displace other adsorbed organics such as pesticides.viii Therefore, we estimate the capacity of charcoal to adsorb
DOC in general, assuming a modest propensity for adsorption on the part of the charcoal and a generous
concentration of DOC in the local water supply.
Conservatively assuming 10 mg DOC/g charcoal as the adsorption capacity of charcoalix and 50 mg DOC/L as the
DOC concentration in natural surface watersx, we estimate that 5 grams of charcoal are needed to sufficiently purify
DIY Water Purification
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1 liter of water. With this ratio, and assuming the EPA recommended daily water intake of 2.5 liters per person per
day, roughly 4.5 kilograms (about 10 lbs.) of charcoal are required to supply drinking water to one person for one
year.

Design for a gravity-fed system will employ a sand pre-filter followed by pulverized charcoal filter medium
supported on a bed of gravel. Exposure to UV radiation after filtration will neutralize biological
contaminants. A photovoltaic panel provides electricity for the UV lamp.
Conservative estimates suggest that the sand layer should be about 50 centimeters thick. The sand acts both as a prefilter
to remove particulates and to precipitate aqueous iron complexes, which can interfere with UV disinfection.xi
A diffuser plate is placed over the sand to reduce the turbulence of the influent and prevent channels forming
through the sand. The thickness of the charcoal layer will depend upon how many people are using the system as
well as its desired lifetime (i.e. the time until the charcoal has to be replaced). The purpose of the gravel layer is to
prevent clogging of the perforated pipe by carbon granules – this layer need only be about 20 centimeters in
thickness.

the attached pdf file shows a basic schematic combining a sand charcoal fiter with a uv purification system

Thats a really good looking system, Thanks for the post.