Secondary disinfection provides an essential residual that prevents the regrowth of microorganisms in the distribution network. Chlorine, chloramines, and chlorine dioxide are commonly used as secondary disinfectants. However, chloramine is the most commonly used secondary disinfectant. Chloramine is not virucidal and is only slightly effective in killing Giardia cysts.

The impact of plastic pipes on water quality in household plumbing and water distribution systems causes leakage of metals such as lead into drinking water. Lead, as the most widespread heavy and toxic element in the environment, is naturally present in river water at a level of 1 to 10 micrograms per liter. Lead compounds enter water sources as a result of mining, battery manufacturing, fossil fuel, paint, and glass and enamel industries.