This last year, we tested the water from our rain water harvesting systems. We found that unfiltered rain water is cleaner than bottled water. In some cases we have the ability to pipe ground water into our rain water harvesting tanks. In these cases, we arm our Rain Catchment System with a slow sand filter. This strengthen's our ability to put an end to the water crisis. This type of filter removes 99.99% of disease, bacteria, viruses, cysts, turbidity, sand, silt, and parasites. It gives the recipients the ability to flush other water sources through the filter and ultimately end up with a perfectly clean water supply. Shockingly, in Africa, very few people boil the water before drinking it. It is an issue of economics and energy. If you can afford the $1.50 per week for coal to boil the water, then you do. If you can afford the extra energy required to fetch what is lost through evaporation, than you do. Truth be told, most do not. The result is a slew of intestinal disease that can now be prevented. Save the Rain chooses to use a Slow Sand Filter because it requires no electricity, chemicals or cartridges or moving parts and requires little to no maintenance but once every 10 years. The maintenance of the filter is simple and requires no special tools or skills.

How Does Slow Sand Filtration Work?

A Slow Sand Filter can be as small as a 2’ diameter by 3’ in height ferro cement or polyethylene container that sits between the water source (or in our case the Rain water tank) and a clean holding tank. This filter can produce between 300 to 64000 gallons of clean drinking water per day. This filtration is a biological process that cleans water much the way the sandy bed of a river does. In the smallest filter, a column of water continually passes through a three-foot layer of fine sand at a specific rate. On the top of the sand, an intense layer of microbes naturally develops. This layer lives by consuming whatever is passing through in the water. A ripening period is necessary for the microbes to grow. This is variable depending on raw water quality, season and temperature. As the water passes through the deeper layers of the filter, other processes such as sedimentation, mechanical filtration, and electrical attraction remove still more.

"Under suitable circumstances, slow sand filtration may be not only the cheapest and simplest but also the most efficient method of water treatment. Its advantages have been proved in practice over a long period, and it is still the chosen method of water purification in certain highly industrialized cities as well as in rural areas mid small communities. It has the great advantage over other methods that it makes better use of the local skills and materials available in developing countries, and it is far more efficient than rapid filtration in removing bacterial contamination."

World Health Organization's Water Sanitation and Health Division

A Slow Sand Filter is the most appropriate way to provide clean drinking water to rural areas of developing countries. Using biological and physical methods, carbon (GAC) in the filter-bed media, the slow sand filter will meet European standards for pesticide removal and remove a number of industrial chemicals, including petroleum byproducts like VOC (volatile organic carbon) and chlorine-disinfectant byproducts (THM, trihallomethanes).