Rainwater- the purest form of water

Māori call harvested rainwater Waiora and is the purest form of water before it touches the earth. They are not wrong; rainwater harvesting is often promoted as a viable alternative to contaminated groundwater. However, rainwater can become easily contaminated by bacteria through storm water. Not a problem though – this is often solved with simple methods like bleaching.

But could there be more than bacteria contaminating the water?

Researcher Riley Mulhern’s work suggests that we should be more worried about the quality of rainwater than we think. Mulhern and a collaborative team decided to test the quality of water captured in rainwater harvesting systems in a remote mining region of the Bolivian Andes. The team, made up from the Centro de Ecología y Pueblos Andinos (CEPA), Comité Académico Técnico de Asesoramiento a Problemas Ambientales (CATAPA), and Mennonite Central Committee, were curious about rain water quality in the region and wanted to know what could be contaminating the harvested rain water.

Installing a rainwater harvesting tank in the Bolivian altiplano. Photo: Maggie Mulhern

Installing a rainwater harvesting tank in the Bolivian altiplano. Photo: Maggie Mulhern

The results didn’t bring good news…

It wasn’t just bacteria that they found. In fact, they found dangerous heavy metals present. With the rise of air pollution from the likes of heavy industry, for example, dust rich in arsenic is being released into the environment and settling on roofs and ending up in harvesting tanks. Over the course of their study, arsenic concentrations in every tank tested were above the World Health Organisation drinking water limit of 10 parts per billion (ppb).

Arsenic can be seriously dangerous. In its inorganic form, arsenic is a known carcinogen – it is not a good idea to consume it!!!

Short term effects of consuming arsenic include a variety of symptoms such as vomiting and muscle cramping, and even death. 

Long term exposure to arsenic – for example drinking water contaminated with it on a daily basis – can cause skin lesions, cancers, heart defects, pregnancy complications and infant mortality, and learning disabilities.

Arsenic poisoning is something we see on a huge scale in South Asia, notably in Bangladesh, where arsenic in drinking water supplies has prompted the World Health Organisation to state it is ‘the worst case of human poisoning in history’.

No one knew that arsenic was present in the groundwater supplies until many hundreds of thousands of people were seriously ill with a variety of health problems. You can’t see or smell arsenic in water, and in the case of Bangladesh no one thought to test for its presence before drilling thousands of boreholes across the country.

Given what we know about the effects of arsenic in drinking water supplies, and of the arsenic found in the Bolivian study, we think testing for arsenic needs to be mandatory for any drinking water project.

Water quality testing

Currently, most standard procedures for checking rural drinking water quality don’t usually include testing for arsenic, apart from in areas where it is known to be a contaminant. The study from Bolivia suggests that there is potential for other trace metals like lead, mercury, chromium and others to be present in rainwater and rainwater harvesting tanks, and we should be more vigilant about assuming that water is safe to drink.

As we’ve said before, just because water looks safe to drink doesn’t mean it is! By striving to make all drinking water safe, for all people, at all times we at Clean Water Wave think we all should be pushing the boundaries of water quality, and ensuring safe water truly means it is safe to drink – wherever you live.

For the full article click on the link: https://www.engineeringforchange.org/news/harvesting-rainwater-test-arsenic/