water supply lasting less than 24 h per day in 44 of the 102 countries included in the database (Danilenko et al., 2014). In 2000, the World Health Organization (WHO) estimated that 60% of the population served by piped water in Latin America and the Caribbean were served by Intermittent Water Supply (IWS) and that at least one in three urban water supplies in Africa and one in two in Asia operated intermittently (WHO, 2000). Overall, 1 billion people suffer from IWS according to WHO/UNICEF Joint Monitoring Program for Water Supply, Sanitation and Hygiene (JMP).

The impact of intermittent water supply is significant, particularly on poor households. Health impacts caused by water disruptions tend to be more severe for low-income households and affect households that consume tap water (Ercumen et al., 2015; Jeandron et al., 2015; Nygård et al., 2007). In India, Ercumen et al. (2015) look at the relationship between water supply interruptions and waterborne illnesses using panel dataset with matched cohorts of households. The impact of water supply interruptions on child diarrheal illnesses depends on household income. Children from low-income households with continuous water supply have 37% lower prevalence of infectious diarrhea than lowincome households with intermittent supply. In higher-income households, there is no significant evidence of the impact of continuous water supply on child diarrheal illnesses, compared to intermittent supply. Results also show that households with continuous water supply report 42% fewer cases of typhoid fever than households with intermittent water supply, regardless of their level of income.

<mark>Studies using official information on water outages and clinic admission data identify a strong and consistent relationship between outages and health impacts.</mark> In the Democratic Republic of Congo, Jeandron et al. (2015) link water interruptions to increased cholera incidence rate using time series data combining admission information from a Cholera Treatment Center and daily variations of water supplied by the water treatment plant. They find that the suspected cholera incidence rate typically increases by 155% over the next 12 days following one day of outage, compared to the incidence rate following optimal water provision. Ashraf et al. (2017) find that water outages in Lusaka, Zambia, are associated with increased incidence of a number of diseases, such as diarrhea and respiratory infections.

Case studies of specific water disruptions also find significant impacts of health. Huge diarrhea outbreaks caused by cholera and _Escherichia coli_ infections are observed after floods (Ahern et al., 2005; Qadri et al., 2005). Diarrheal pathogens can spread through direct contact with floodwater or through compromised water sources. However, their impact is temporary and prevalence of diarrhea in exposed and non-exposed groups are equal in the long-run (Joshi et al., 2011). A case study from Alabama, US, looks at the effect of a freeze-related water emergency on diarrheal and respiratory illnesses. The researchers find a significantly higher risk of contracting diarrhea for households experiencing water disruptions and low water pressure and prevalence increases with the length of disruption (Gargano et al., 2015). The diarrhea outbreak in Milwaukee which affected 403,000 individuals, was caused by a filtration system that malfunctioned after a heavy storm releasing the bacteria _Cryptosporidium oocysts_ in the water distribution system (Hoxie et al., 1997; Mac Kenzie et al., 1994).

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