Household water treatment systems
Practical Action
Storage
The approach to storage can also help with treating the water in that a carefully designed
system with a slow flow of water from the inlet to the outlet will allow the water to settle and
provide enough time for pathogens to die off. The water should be stored for 48 hours in a
covered tank.
The book Environmental Health Engineering in The Tropics states that “for storage tanks a
few small leaks in a tank above ground may not be serious in village circumstances, and
perfectly adequate tanks may be built of local building materials such as brick or masonry,
especially if galvanized wire is laid between courses to give the walls horizontal
reinforcement.” The tank should be protected so that it doesn’t become a breeding ground for
mosquitoes which means it should be covered, have ventilation pipes screened with mosquito
proof mesh and steps should be taken to avoid breeding sites downstream from the overflow.
Sand filters
Sand filters can work well if they are maintained but this is a difficult task and is often
neglected which means that the filters often don’t work. It is best using a system where
filtering can be done easily and maintenance is not going to become an issue. In some cases
that might mean a disposable or replaceable filter or a ceramic filter if these are available
from a nearby source. In many cases this will not be a realistic option and alternative
approaches need to be considered.
Slow sand filters (velocity of 0.1 to 0.2 m/hr) are one approach for household applications.
Different grades of sand can filter out physical impurities and can also eliminate pathogens
as they develop a layer of algae, bacteria and fungi that feed on the harmful microorganisms
in water. This biofilm is called a schmutzdecke. Sand filters will block up over time with
inorganic matter but this can be cleaned out by backwashing. Inorganic matter can be
removed through rough filtering or by using sedimentation tanks.
Slow sand filters improve the microbiological quality of the water but do not provide
completely clean water and an additional treatment such as chlorination of UV is often
needed.
Simple slow sand filters can be constructed with an old oil drum and can be upward filter
systems or downward filter systems.
Sand filter systems are described in the document Slow Sand-Filtration Water Treatment
Plants produced by Soluciones Prácticas.
This document focuses on household water treatment systems using the slow-sand water filter
approach. Some construction guidelines are available at the following website
http://www.biosandfilter.org/biosandfilter/index.php/item/330
Ceramic filters
The American Red Cross developed a ceramic water filter in Sri Lanka which seems to be
technically very good. The design is aimed at family level water treatment. Practical Action
has a fact sheet about this which can be seen at The Clay Water Filter
2