Water supply and sanitation services are important for a whole host of reasons – time saving, dignity, convenience, economic growth, – including of course, public health. Yet it remains difficult to evaluate the extent to which those services actually do change health outcomes. Public health is affected by many variables, which interact in complex ways. In addition, the quality of water people consume and their exposure to fecal pathogens are affected by a complex set of factors based on individual and household practices, as well as the service standards of water and sanitation providers.
One recent study illustrates how much the quality of service matters. A team of researchers from the University of Göttingen  (Germany) has used rigorous statistical techniques to evaluate a large-scale project in urban Yemen that provides household connections to piped water and sewerage in eight provincial towns throughout the country, including Amran in the mountains and Zabid in the coastal Tihama region, which were selected for the analysis together with nearby comparison towns.
The result is completely counterintuitive. The study finds that when households in the focus cities were connected to the piped water network, the likelihood of their getting diarrhea and the severity of each bout of diarrhea worsened. When they also had a household connection to sanitation, both worsened further. The effect was particularly strong among children under 5 years of age. Why would this be? The water released by the water treatment plant is clean. However, the water delivered to household is not. It’s getting contaminated in the pipes between the treatment and the household. Because the pipes are empty for more than half of the time they corrode fast and contaminants are introduced. The study  finds that more than half of the worsening of health outcomes can be attributed to the piped water network.
Although Yemen is one of the most water stressed countries in the world, intermittent water supply is common in many parts of the developing world and especially in the Middle East, with largely unknown consequences on water quality and health outcomes. This research is therefore potentially relevant to many towns in the region.
What does this mean for development policy?
First, we need to worry not only about access to water and sanitation services, but also about quality of service. Second, we need to understand more explicitly the costs of poor service in terms of public health, household coping strategies (e.g. bottled water, storage tanks, etc.) and in terms of additional wear and tear on the network infrastructure. Third, where intermittent supply is likely to be a reality in the short to medium term, we need to think about interim solutions. These might include water purification at the household level, and could also mean alternative supplies, such as water trucks and other water vendors.
Truck water is currently not considered an improved drinking water source in the UN’s Joint Monitoring Program. It would be useful to conduct some rigorous studies to identify the extent to which truck water can provide a safe source of drinking water as an interim solution. If we can ensure the safety of supplies from trucks, they hold potential given that they do not require network infrastructure investment, are low cost, are flexible to changing ground water levels, and water vendors already exist throughout the MENA region.
Klasen et al (2012) Benefits trickling away: The health impact of extending access to piped water and sanitation in urban Yemen. Journal of Development Effectiveness 
Lechtenfeld (2012) Why does Piped Water not reduce Diarrhea for Children? Courant Discussion Paper, University of Göttingen, Germany