Arsenic detected in rainwater harvesting tanks in Bolivia

This is a guest blog by Riley Mulhern, a PhD student at the University of North Carolina. If you are interested in issues related to water quality monitoring, you can join our online community here.  

In areas of water scarcity around the globe, made worse by climate change and pollution of groundwater, rainwater harvesting remains an important source of water supply for rural communities.

This is especially true in the Bolivian altiplano, where drought and mining work together to create pockets of severe water stress in what is generally considered a water-rich country. I lived among these communities high in the Andes for two years working with an organization called the Centro de Ecología y Pueblos Andinos (Center for Ecology and Andean Peoples, or CEPA). I assisted CEPA with a small-scale rainwater harvesting project for rural communities with high needs.

Over the course of the project, CEPA monitored the quality of harvested rainwater through consecutive wet and dry seasons. Surprisingly, we detected arsenic in every tank we monitored, 18 in total, whereas no microbial contamination was found.

This finding alerted CEPA to the risk of rainwater contamination in the region. Further testing identified roof dust that flushes into the tanks from the roof catchment as the principle source of arsenic in the rainwater. No arsenic was detected in raw rainwater before it interacted with the roof or tank. The source of the arsenic in the dust, whether naturally elevated in the altiplano soil or mobilized due to mining activity and released into the environment, is unknown, but widespread mining contamination in the area is likely a contributor.

Given these findings, the implementation of rainwater harvesting as an alternative drinking water supply by nonprofit groups and charitable organizations without adequate monitoring and evaluation of water quality is a potential concern. Since rainwater is presumed to be arsenic-free, rainwater harvesting has been promoted as an alternative drinking water source in other areas affected by arsenic contamination of groundwater as well, such as Mexico, parts of Central America, and Bangladesh. It is not safe to assume rainwater will be entirely arsenic-free, however. The levels found in collection tanks in Bolivia were double the WHO health guideline of 10 parts per billion.

As a result, arsenic and other metals should be included as standard monitoring parameters in rainwater projects. Groups implementing rainwater harvesting projects should seek additional partners with the tools and knowledge to perform thorough water quality testing.

This can be accomplished either through basic field tests, which provide semi-quantitative information for initial screening, or through laboratory analysis. Research done at North Carolina State University found that the standard field method—where inorganic arsenic in a water sample is reduced to arsine gas, which then reacts with a mercuric bromide strip to turn color—tends to underestimate the actual arsenic concentration as verified by ICP-MS (a sophisticated method that detects counts of atoms in a sample at specific molecular weights, allowing for a precise quantitative measurement). However, these low-cost and easily transportable kits still offer an accessible and simple screening tool for the presence of arsenic. The ITS Econoquick, for example, provides 300 tests with a 0.3 ppb detection limit for less than $200. For more precise measurements and longer term use, the Palintest Arsenator includes a standardized digital reading of the colorimetric output for $1,200. Both kits were field tested by CEPA and were easy to use for untrained operators.

In addition to greater testing, practitioners should also consider the required first flush volume for their project. First flush systems are essential for any rainwater harvesting scenario to mitigate both microbial and chemical risks. This is especially true when used as a drinking water source. One rule of thumb is that first flush systems should be able to capture at least 4 liters of water for every 10 square meters of roof. The tanks monitored in Bolivia did not meet this standard. Thus, the risk of arsenic contamination of rainwater and simple controls for system design and monitoring should also be communicated widely through knowledge platforms such as RWSN and the RAIN Foundation.

The results of this monitoring study were compiled by CEPA and a Belgian organization, the Comité Académico Técnico de Asesoramiento a Problemas Ambientales (CATAPA). The full results have been published and are accessible through the journal Science of the Total Environment. This work has also been featured previously by

About the author

Riley Mulhern is a PhD student at the University of North Carolina Chapel Hill Gillings School of Global Public Health. He worked previously as a technical water quality adviser for a Bolivian environmental justice nonprofit addressing issues of mining contamination in rural indigenous communities in Oruro, Bolivia. He is from Denver, Colorado and received his B.S. in physics and geology from Wheaton College in Wheaton, IL and M.S. in Environmental Engineering from the University of Colorado Boulder. He has worked previously on water projects in Nicaragua and Haiti.

Photo: Rainwater tank monitored for the study being installed. Photo credit: Maggie Mulhern.



And the winner is… or the tale of how difficult it is for a young professional from Sierra Leone to attend World Water Week

We were very happy to announce Benson Kandeh’s nomination as the winner of the RWSN@WWW competition last month. However, we unfortunately received the news that Benson will be unable to attend the SIWI World Water Week conference, as he was denied a visa to travel to Sweden. This is a huge disappointment to him and to us.

We thought we should take this opportunity to highlight the hurdles that Benson, and other young professionals like him, have to overcome to attempt to attend a conference in Europe or North America. As development professionals, we should aim to cater and build capacity in-country in the water sector, and especially for young professionals. Conferences, workshops and training courses are crucial for building professionalism. Benson’s story highlights how difficult it is for a young professional from a fragile country, such as Sierra Leone, to attend the most important annual global conference in the water sector in development.

The issue is not only to do with the fact that he was not granted a visa – the difficulties for him to obtain this visa in the first place were prohibitively expensive and time consuming. The only place for Sierra Leone nationals to apply for a visa to Sweden are Nigeria and Morocco – and they have to apply in person. Benson had to travel more than 2,000 kilometres from Freetown to Lagos, and put his life on hold while waiting for a decision on his visa in a foreign country for almost two weeks. Admiringly, Benson managed to make the most of his trip by working on improving an unprotected well in the community where he was staying in Lagos.

The problem is not limited to the water sector: African academics and development professionals face arbitrary decision-making by immigration authorities. In the UK, the Royal African Society has compiled a number of disturbing findings about the barriers faced by African professionals. However, as development professionals, we have an obligation to ensure that we are building capacity in developing countries. This is why we are proud to have organised the RWSN Forum in low- and middle-incomes countries since its first handpump technology workshop in Kenya in 1992 and most recently in Côte d’Ivoire in 2016.

In the face of increasingly toxic political discourse on immigration, it is incumbent on all of us not to turn a blind eye, but communicate the benefits of international and intercultural exchange and cooperation and put pressure on over-zealous immigration authorities. In parallel, international development events should be organised where they are most needed and most accessible, to allow more water professionals like Benson to participate in international development conferences.

UPDATE! (from the RWSN Secretariat): We lodged an appeal against the decision to deny Benson his visa with the Swedish migration authorities. The Swedish embassy in Abuja overturned the ruling based on our appeal on 16th August, and this decision was upheld by the Swedish court. Benson should therefore be able to get his visa and attend World Water Week – so watch this space for updates from our winner!