D. Brett Martinson and Terry Thomas
11th International Rainwater Catchment Systems Conference, Texcoco, Mexico, 2005
The quality of water in a rainwater tank is a matter of much speculation, however several techniques can be used to protect and enhance the quality. If these procedures are followed, tank water should conform to the World Health Organisation’s “Low Risk” category.
The primary contamination pathways are via vectors (such as lizards or frogs) directly entering the tank and via inlet water.
This first of these is easily blocked for larger animals by screening all inlets and overflows. A more important path is via the water entering from the roof. As water passes through the air, onto the roof and flows to the tank, it picks up contamination and carries it into the tank. The contaminants tend to adhere to solid matter that is washed along with the water flow and can be filtered using simple techniques. There is also substantial evidence that water quality improves with time, therefore any system that prevents contaminated water from
interacting with “aged” water in the tank will also enhance water quality.
This paper discusses inlet and outlet arrangements for water tanks that can easily be incorporated in low-income countries, yet will substantially enhance water quality both by preventing contaminants from entering the tank and by aiding natural water purification occurring in the tank. A brief discussion is also offered on system maintenance for quality enhancement.