Tap water quality varies enormously from country to country, city to city, neighborhood to neighborhood, and even from block to block. Tap water distribution systems can be leaky and are often low pressure systems in order to save pumping energy costs. They can therefore siphon contaminants from adjacent and also often leaky sewage pipes, drainage ditches, gutters, and surface water bodies.
Tap water is often delivered under very low pressues and delivery is often irregular sometimes just a few hours per day.
As such, tap water may be fine when it leaves a municipal treatment plant, but it may be highly contaminated by the time it reaches the point of use. In some localities it may also be so strongly chlorinated that consumers do not like to drink it.
This Chinese family does not drink tap water but they use it for many other tasks
Tap water in Seoul is safe to drink, but many families use products to improve it
An outdoor tap for laundry, dish washing and other tasks in Mexico City
For many people, including this girl fetching water from a public pump, tap water is not available