Originally published on Sphere (24 April 2026)

Authored by Dahdaleh Research Associate James Brown

Providing safe drinking water is a core priority in humanitarian response. Sphere Water Supply Standard 2.2: Water quality (“WASH Standard 2.2”) states that “water is palatable and of sufficient quality for drinking and cooking, and for personal and domestic hygiene, without causing a risk to health”.

Meeting this standard in practice is not always easy. Water systems in humanitarian settings operate under highly variable conditions, including changing source water quality, intermittent pumping, and widely varying household water handling practices. In these contexts, applying fixed water quality targets can lead to outcomes that fall short of the standard’s intent^[1],[2].

Moving beyond fixed targets

Sphere guidance includes indicative targets for water quality, including for free residual chlorine (FRC) at the point of delivery. These targets provide an essential reference point, but they do not capture all the factors that influence whether water remains safe to drink at the point of consumption—where it most matters for public health.

In many humanitarian settings, even water that meets recommended FRC levels at the point of delivery can lose its protective residual during collection, transport, and household storage and use, which can extend for 24 hours or even longer in some situations. Numerous studies now show that recontamination of water is linked to spread of waterborne diseases^[3],[4],[5]. Furthermore, greatly increasing chlorine doses to compensate for this decay can lead to taste and odour concerns that discourage people’s use of treated water supplies, often leading them to turn to unsafe sources in the surrounding environment. Water system operators are left having to balance water safety and user acceptability with limited evidence to guide their decisions.

The Safe Water Optimization Tool (SWOT) addresses this gap by using routine water quality data to model how water quality changes across the full water supply chain. This allows operators to set chlorination targets that are specific to their own systems, rather than relying on universal standards that do not reflect local conditions.

The SWOT has been implemented across a wide range of water system types common in humanitarian settings, including piped networks, water trucking systems, and institutional/healthcare facility water systems, using both groundwater and surface water sources. Field evaluations demonstrate that the SWOT can improve the efficacy of safe water programs by 50-200% or more, offering a powerful way to ensure the public health impact of safe water programs^[6],[7].

Experience from Uganda

Work in the Kyaka II refugee settlement in western Uganda illustrates how the SWOT approach can support WASH Standard 2.2 in practice. Kyaka II is served by a large surface water treatment system supplying water through a piped network to public tapstands. Source water quality varies, and long distribution times and high temperatures increase chlorine decay.

Using data already collected by the water supply team, the SWOT was applied to examine whether existing chlorination practices were sufficient to control microbial risks up to household use. The analysis showed that, under some conditions, higher chlorine doses at the treatment plant were needed to maintain protection through storage. At the same time, structured testing with water users highlighted that acceptability varied depending on water source and prior exposure to chlorinated water.

By combining these insights, operators were able to adjust chlorination practices in a way that improved public health protection while responding to users’ taste and odour concerns. This supported a more balanced and transparent approach to meeting Sphere’s water quality standard.

Supporting better operational decisions

The SWOT is designed to support day-to-day decision-making by water system operators. It helps answer practical questions such as:

• Are current water treatment practices likely to protect water all the way up to when and where it is consumed?
• Where in the system is the chlorine protection being lost most rapidly?
• What is the appropriate chlorine dose to balance water safety and user acceptability?

By focusing on outcomes rather than on fixed inputs, the SWOT helps achieve the Sphere standards by enabling evidence-based operational decisions that reflect local conditions.

Looking ahead

Current water quality monitoring relies heavily on proxy indicators such as chlorine residuals. While essential, these do not directly describe health risk. Ongoing research is exploring how the SWOT can be extended to estimate health risks directly from easy-to-measure water quality data by bringing together quantitative microbial risk assessment and machine learning techniques.

This work aims to further strengthen the link between water quality monitoring and the public health outcomes that the Sphere standards are intended to protect.

A practical way to contextualise Sphere

The Safe Water Optimization Tool does not change the Sphere standards. Instead, it gives field teams the means to achieve them in diverse and highly complex humanitarian settings. By moving beyond non-evidence-based, one-size-fits-all targets toward context-specific, data-driven decision-making, the SWOT offers a practical way to uphold WASH Standard 2.2 and ensure that safe, acceptable water reaches people where and when they need it most.

Contact the author: brownje@yorku.ca

See also: Measuring water sufficiency through people’s experiences: using the WISE Scales to support WASH Standard 2.1

Safe Water Optimization Tool (SWOT): https://www.safeh2o.app/

[1] Ali, S. I., Ali, S. S., & Fesselet, J. F. (2015). Effectiveness of emergency water treatment practices in refugee camps in South Sudan. Bulletin of the World Health Organization, 93(8), 550–558. https://doi.org/10.2471/BLT.14.147645

[2] Ali, S. I., Ali, S. S., & Fesselet, J.-F. (2021). Evidence-based chlorination targets for household water safety in humanitarian settings: Recommendations from a multi-site study in refugee camps in South Sudan, Jordan, and Rwanda. Water Research, 189, 116642. https://doi.org/10.1016/j.watres.2020.116642

[3] Swerdlow, D. L.; Malenga, G.; Begkoyian, G.; Nyangulu, D.; Toole, M.; Waldman, R. J.; Puhr, D. N. D.; Tauxe, R. V. Epidemic cholera among refugees in Malawi, Africa: treatment and transmission. Epidemiology and Infection 1997, 118 (3), 207–214.

[4] Walden, V. M.; Lamond, E.; Field, S. A. Container contamination as a possible source of a diarrhoea outbreak in Abou Shouk camp, Darfur province, Sudan. Disasters 2005, 29 (3), 213–221.

[5] Roberts, L.; Chartier, Y.; Chartier, O.; Malenga, G.; Toole, M.; Rodka, H. Keeping clean water clean in a Malawi refugee camp: a randomized intervention trial. Bulletin of the World Health Organization 2001, 79 (4), 280–287.

[6] Camille Heylen, Gabrielle String, Doreen Naliyongo, Syed Imran Ali, James Brown, Michael De Santi, Vincent Ogira, Jean-François Fesselet, James Orbinski, and Daniele Lantagne. (2024). Evaluation of the Safe Water Optimization Tool to Provide Evidence-Based Chlorination Targets in Surface Waters: Lessons from a Refugee Setting in Uganda. Environmental Science & Technology 58 (42), 18531-18540 https://doi.org/10.1021/acs.est.4c04240

[7] Ali SI, De Santi M, Arnold M, Khan UT, Penney TL, Ali SS, et al. Proof-of-concept evaluation at Cox’s Bazar of the Safe Water Optimization Tool: water quality modelling for safe water supply in humanitarian emergencies. BMJ Global Health. 2025;10:e018631. https://doi.org/10.1136/bmjgh-2024-018631

You may also be interested in...