The risk of contamination of drinking water supplies with microbiological pathogens can be minimised by modern approaches to water management but continues to be a major public health concern.
Environmental issues such as global warming are likely to affect sustainability of our drinking water supplies.
The use of alternative water sources such as roof-collected rainwater can be part of the solution to diminishing water resources but have the potential to introduce new health threats such as waterborne disease outbreaks.
Rainwater collection for drinking and other domestic uses is practised by individuals in almost every country in the world and since most modern rainwater collection systems are upgraded or modified forms of traditional technologies, they offer the potential of providing sustainable water supplies with low cost environmental impact.
Rainwater is especially valued as a drinking water source when alternative sources such as town-reticulated supplies are not available or when alternative sources are of poor chemical (e.g. ground water salinity) or bacteriological quality (particularly surface waters).
Although rain tends to be seasonal, rainwater can provide a convenient alternative water source when rains are abundant.
Rainwater use is also becoming popular because of the public’s perception that rainwater is "pure" and that municipal water contains too many harmful chemicals.
For domestic water consumption the most common method of rainwater collection is by channelling water from the roof into large tanks made of various types of material. Providing the rainwater is clear, has little taste or smell and is collected from a well-maintained system, it is probably safe and unlikely to cause any illness in most users.
While rainwater itself is free from pathogens and contamination levels of stored rainwater are generally low if tanks are well protected with covers or lids, obvious sources of contamination of the rainwater runoff from roofs and gutters are from birds, lizzards, rodents, and rotting vegetation.
Tank rainwater can contain organisms referred to as opportunistic pathogens such as Aeromonas spp and Pseudomonas aeruginosa .
Several overseas investigations in the 1980s raised concerns when they revealed that in many instances stored rainwater did not meet WHO, EPA or other similar standards with respect to one or more bacteriological water quality indicators (Fujioka & Chinn, 1987; Haebler & Waller, 1987; Krishna, 1989). In northeast Thailand, where several million people use rainwater tanks, a major study of rainwater quality by Wirojanagud et al. (1989) on 189 rainwater storage tanks, revealed that only around 40% met WHO drinking water standards. The results of the indicator organism counts from the water samples from roofs and gutters indicated that the faecal contamination was from non-human sources such as animals, birds and rodents.
Micro-organisms from the roof or gutters also build up in the sludge layer
Sludge is a build-up of a variety of small particles at the bottom of a tank. It can consist of:
• vegetation debris from nearby plants and trees
• faecal matter deposited on water catchment areas by birds lizzards, rodents etc.
• air-borne pollution - dust, smoke, chemical
• roof & gutter material breakdown, including flaking paint and iron
Sludge generally contains bacteria and can be a potential health risk whether you are drinking the water or using it in the garden or laundry.
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