- Untreated rain water from well maintained roofs is generally safe to drink. Consumption of rainwater collected from ground catching systems without treatment is not recommended due to high levels of microbial contamination.
Untreated roof runoff has been widely used for drinking purposes for many years with very few reports of serious health problems. While health risks may be small, recent findings suggest there is little room for complacency and every effort needs to be taken to minimize rainwater contamination. Compared with most unprotected traditional water sources, drinking
rainwater from well maintained roof catchments usually represents a considerable improvement and even if it is untreated it is generally safe to drink.
A number of pathogens harmful to health and disease outbreaks linked to rainwater sources have been documented. While serious, these outbreaks are all isolated and comparatively rare incidents. Nevertheless, they do provide an important warning regarding the potential hazards associated with drinking rainwater from sources which are poorly located, constructed or maintained.
Keeping leaves and organic material from accumulating in the tank and gutters will also help to prevent the stored rainwater from becoming too acidic and potentially leaching lead or other heavy metals from the tank walls, fittings or sludge deposits into the water. Source: Is rainwater safe to drink? A review of recent findings
- Inadvertent or accidental drinking of small quantities of rainwater is highly unlikely to cause adverse health effects.
Of the epidemiological studies conducted on rainwater to date, 2 have compared rates of gastroenteritis between populations of children (presumably a more susceptible population), and these unblinded studies showed no increased risk of illness associated with rainwater consumption. Our blinded study supports this conclusion and further indicates that adults have no increased risk of illness. Our results therefore suggest that consumption of untreated rainwater does not significantly contribute to community gastroenteritis incidence. This has important implications: at a minimum, inadvertent or accidental ingestion of small quantities of rainwater during showering and other water usage activities is highly unlikely to cause adverse health effects. Source: Drinking Rainwater: A Double-Blinded, Randomized Controlled Study of Water Treatment Filters and Gastroenteritis Incidence.
However, caution is advised for elderly and immune-compromised individuals when drinking untreated rainwater collected from roofs due to presence of pathogens.
Current estimates of health risk suggests that it would be prudent to disinfect roof-harvested rainwater, such as by the installation of a UV disinfection unit, boiling, or other forms of disinfection, before using it as potable water, especially for drinking. This would be especially prudent for the elderly and immunocompromised. Maintenance of good roof and gutter hygiene and elimination of overhanging tree branches and other structures where possible to prevent the congregation of animals are also recommended. Inclusion of giardiasis in the notifiable disease list in Queensland should be considered, given that G. lamblia was found in rainwater tank samples. Source: Health Risk from the Use of Roof-Harvested Rainwater in Southeast Queensland, Australia, as Potable or Nonpotable Water, Determined Using Quantitative Microbial Risk Assessment
At least 50% of the roof-collected rainwater samples from private dwellings exceeded the minimal acceptable New Zealand standards for contamination and 41% of the samples showed evidence of heavy faecal contamination. The likely sources of the faecal contamination were faecal material deposited by birds, frogs, rodents and possums, and dead animals and insects, either on the roofs or in the gutters, or in the water tank itself.In a significant number of supplies where we found heavy faecal contamination there was evidence of lack of maintenance; inadequate treatment of the water; poorly designed delivery systems and storage tanks; and failure to adopt even simple physical
measures to safeguard the water against microbiological contamination.
Many of the organisms that have been isolated from contaminated roof water have the potential for human pathogenicity, which under certain conditions can lead to infection and possibly disease outbreaks, notably gastrointestinal diseases from pathogens such Salmonella,
Campylobacter, Giardia and Cryptosporidium. Source: The microbiological quality of roof-collected rainwater of private dwellings in New Zealand