In poor developing countries (Pakistan included), sewer lines clogging is common. In fact, currently in Karachi, a number of sewer lines are clogged, forcing sewage to overflow. Sewage overflows pollute water sources. In rural areas of Pakistan, pollution of water bodies by sewage is common.
A recent paper: Sanitary Sewer Overflows and Emergency Room Visits for Gastrointestinal Illness: Analysis of Massachusetts Data, 2006–2007, available at:
quantifies the health aspect of sewer overflows. Sewer overflows was examined in association with emergency room visits for gastrointestinal (GI) illness.
Tracing the history of sewerage system in USA, the paper says:
“Water infrastructure in the United States is aging, and many, older cities in the United States have infrastructure that needs to be upgraded. The U.S. Environmental Protection Agency (EPA) estimates that the majority of the nation’s sewage collection infrastructure is between 30 and 100 y old, putting it at risk for leaks, blockages, and malfunctions due to deterioration (U.S. EPA 2000). This aging water infrastructure is vulnerable to changes in weather that are expected to occur with climate change (Patz et al. 2005, 2008). In particular, the expected changes in precipitation events and increases in heavy rainfall events can have negative impacts on water infrastructure. Heavy rainfall events can overwhelm these systems, causing untreated waters and sewage to be released into receiving waters.”
The paper demonstrates an association between sanitary sewer overflow events and emergency visits for GI illness using a case-crossover study design. In light of the aging water infrastructure in the United States and the expected increase in heavy rainfall events, our findings suggest a potential health impact associated with sewage overflows.