Is tap water pure

Drinking water from the tap should be suitable for drinking. This is mostly the case except on those occasions when the waterworks are overloaded or surface water enters the drinking water system.
However, even when tap water is at its best there are shortcomings. For a start it contains a strong bactericide, a substance that in concentrated form was once uses as a war weapon, chlorine. This keeps bacteria and viruses under control, usually successfully. When the system fails it becomes front-page news....

Some authorities also add fluorine to the water.
Water also contains chalk, gypsum, minerals and various other foreign substances.
During its transport from the water works via water towers and the water distribution system, the water comes into contact with animals, insects and other organisms. The water mains system is old and during the several days it can take to transport, various substances can leak in. These include poisons from weed killer and insecticides, fertilizers, heavy metals, arsenic, phosphor, pcb’s chromium, sewage and surface water containing dissolved air pollutants such a sulphur and the like, rust and material from the pipes.
For those interested there is a lot of information on drinking water on the Internet. Everything disappears with distillation.