An evaluation of measures for improving the quality of roof-collected rainwater

Rainwater itself is free from pathogens and contamination levels of stored rainwater are generally low if tanks are well protected with covers or lids but obvious sources of contamination of the rainwater runoff can originate from faecal matter deposited by birds, frogs, possums, rodents, and dead animals and insects, either on the roofs or in the gutters, or in the water tank itself. A number of national and international studies have shown that the microbiological quality of roof-collected rainwater is usually poor, often fails to meet drinking water standards, and frequently there is evidence of faecal contamination in the stored roof water. In a significant number of roof water supplies of private dwellings in New Zealand where we found heavy faecal contamination, there was evidence of poorly designed delivery systems and storage tanks, and failure to adopt physical measures to safeguard the water against microbiological contamination. A variety of low maintenance products and systems are now available in New Zealand for reducing, and in some situations even eliminating, microbial contamination of stored rainwater. In this paper we present the results of a preliminary study in which we evaluated the effectiveness of some of these products and systems. The study involved an intensive microbiological analysis of roof-collected rainwater samples collected over nine months and covered a range of climatic conditions.