New methods for new applications

In this short blogpost series, we are excited to share some of the initial learning from our HIF-funded WASH Evidence Challenge study in Uganda. This post, the second in the series, describes how we’re testing the SWOT out in new water supply use cases, as well as developing new tools for the SWOT toolkit that will provide for a more holistic understanding of water quality.

Surface water in piped networks and water trucking

Kyaka II brings an opportunity to trial the SWOT in an important water supply use case—surface water delivered both via piped network and by water trucking. Compared to groundwater pumped from underground aquifers, surface water is more likely to be contaminated with organic material and chemicals from agricultural runoff or sewage. Turbidity and the chemical composition of water have a significant impact on chlorine decay—even after the water has been clarified. The data we will collect at Kyaka II will enable us to explore differences in chlorine decay between groundwater and surface water sources and adapt the SWOT’s modelling tools to ensure robust FRC (free residual chlorine) guidance irrespective of the water source.

Kyaka II also provides an opportunity to apply the SWOT to water trucking. Water trucking is a common intervention especially during the acute phase of an emergency before piped water networks can be installed, or when additional supplies are needed rapidly or temporarily. Although most areas of Kyaka II are connected to the piped water network, water trucking is used to reach people who are not yet connected. We are interested in learning how well the SWOT’s modelling performs with water trucking, as the drivers of chlorine decay may be quite different from those in a closed, piped system. Our goal for modelling water trucking is to be able to determine the initial dose of chlorine product required to achieve the desired stable residual both at delivery from the truck, and at the household point-of-consumption many hours later.

To collect data to characterize chlorine decay in the piped network and water trucking use cases, we collected paired water samples taken from tapstands and from households, as well as initial chlorine doses in the water trucking system. We also surveyed water users to understand how they collect, store, and use water at home. The paired samples were analysed by the SWOT to provide a tapstand FRC target for the typical storage time determined by the survey. We gathered this data both before and after the water system operator adjusted chlorination levels at the tapstands to meet the SWOT FRC target to understand how effective this recommendation was for improving household water safety.

Chlorine taste and odour

The aesthetic aspects of drinking water quality—the way water looks, smells, and tastes—are critical when it comes to ensuring people are drinking safe, treated water, rather than collecting water from other untreated and possibly contaminated sources. For chlorinated water supplies in humanitarian settings, there is an important balance that must be struck between having sufficient residual chlorine to maintain water safety but not so high that people reject the water because they find it unpalatable.

While the SWOT was developed to model the minimum FRC required to ensure water safety up to the point-of-consumption, we recognise that we must also consider the maximum FRC that is acceptable to the population. The challenge is that, while there is a well-evidenced minimum FRC for water safety, people’s tolerance for chlorine taste and odour in drinking water is very population specific. To help water system operators in emergency settings understand this better, we are developing and testing a new rapid field method for assessing population-specific chlorine taste and odour acceptability thresholds. The method is based upon the triangle test method, widely used in municipal water systems and in food science, with adaptions to make it quicker and easier to carry out in the field.

The results of our taste and odour acceptability tests at Kyaka II were compared to the recommended FRC target generated by the SWOT to produce a target range of FRC that balances water safety and acceptability concerns. Additionally, interviews conducted with the taste test facilitators provided insights into how well the method worked in practice, which will help us improve the method for future field use.

Disinfection by-products

A final component of our research at Kyaka II deals with disinfection by-products (DBPs)— chemicals that are formed when chlorine reacts with organic matter in water. While there is limited evidence about the risks of DBPs in drinking water, there are some indications that long term exposure may be harmful to human health. To date, there is little known about the levels of DBPs people might be exposed to in emergency water systems.

Since DBPs form in the presence of organic matter, they are more likely to be found at higher levels in chlorinated surface water than in groundwater-based systems. The formation of DBPs has not been researched in humanitarian or low-resource settings, in part because testing the concentration of DBPs requires specialist equipment, consumables, and methods. So, we will be testing water both to characterize the levels of DBP present in the treated water, and to compare the accuracy of measurements carried out on site using a field device with gold-standard measurements carried out at a certified lab in the USA. We hope to learn about how practical the measurement process is for field teams to carry out, and to understand how these compare with the gold-standard as a way of charting out a field method for monitoring DBPs.

We hope that testing these approaches to measuring and monitoring distinct aspects of water quality will provide insights about how we can expand the SWOT toolkit to enable field teams to understand water quality in a broader way and better respond to community preferences for their water supply. In the next post we’ll explore some of the initial results and key learnings from the work so far.