Water quality and health risk
Rainwater is relatively free from impurities except those picked up by rain from the atmosphere however, the quality of stored rainwater may deteriorate during harvesting, and storage. Wind-blown dirt, leaves, faecal droppings from birds and animals, insects and contaminated litter on the catchment areas can be sources of contamination of rainwater which can leading to health risks from the consumption of contaminated water from storage tanks. Poor hygiene in storing water can also represent a health concern. However, risks from these hazards can be minimised by good design and practice. Well designed rainwater harvesting systems with clean catchments, leaf guards, downpipes and storage tanks systems can offer drinking-water with very low health risk, whereas a poorly designed and managed systems can pose high health risks.
Microbial contamination of collected rainwater indicated by E. coli (or, alternatively, thermotolerants coliforms) is quite common, particularly in samples collected shortly after rainfall. Pathogens such as Cryptosporidium, Giardia, Campylobacter, Vibrio, Salmonella, Shigella and Pseudomonas have also been detected in rainwater. However,
the occurrence of pathogens is generally lower in rainwater than in unprotected surface waters, and the presence of non-bacterial pathogens, in particular, can be minimized.