Municipal water utilities around the globe face a daunting set of challenges. In high-income countries, they must maintain piped networks that deliver high quality, reliable water supply to homes and remove household waste via piped sewerage networks. In most cities in low-and middle-income countries, they must improve the quality and reliability of services, connect households to the network, and plan for large population influxes. Utilities need financial resources to attack these problems, but tariffs in many places are too low: only 35% of utilities in the World Bank's International Benchmarking Network for Water and Sanitation Utilities database collect enough revenue to cover operations and maintenance costs, and only 14% collect enough to cover the full economic cost of service provision, including the cost of capital (Andres et al., 2019). Support for tariff reforms, however, depends on effectively protecting poor customers. Furthermore, "affordability" is explicitly mentioned in many of the Sustainable Development Goals, including access to "affordable" housing, energy, health care and water and sanitation services. A common policy prescription among water tariff consultants is to balance the objectives of affordability, efficiency and revenue stability with increasing-block tariffs, where the marginal price of water increases with increasing use. Because it is assumed that the highest water users are also the wealthiest, it is commonly believed that this tariff can in theory redirect revenue from wealthier households and cross-subsidize lower rates for low-income households, who are assumed to use less water. In practice, these tariff policies have been shown to do a poor job of directing subsidies to the poor in many low-income countries, in part because the correlation between income and water use is weaker than commonly believed (Burger & Jansen, 2014;Fuente et al., 2016). Utilities are increasingly experimenting with other types of "customer assistance programs" to help the poor (Cook et al., 2020). These include providing a free or subsidized "lifeline" quantity of water to poor customers, a policy that many cities in South Africa have employed as part of the country's Free Basic Water program (