Drinking water or potable water is water safe enough to be consumed by humans or used with low risk of immediate or long term harm. Drinking water, like every other substance, contains small amounts of bacteria. Most of these bacteria are common ones and they are generally not harmful. Chlorine is usually added to drinking water to prevent bacterial growth while the water streams through pipelines. This is why drinking water also contains minimal amounts of chlorine.
If you want to find out what substances your tap water consists of and whether it is totally safe to drink you can have a specialized agency check it out for you.