Potable water means water which is fit for drinking by humans and other animals. It can be consumed with low risk of immediate or long term harm.
Non-potable water is that which is not safe for drinking. It may carry disease causing microbes, and high levels of dissolved salts and minerals, heavy metals and suspended solids. Drinking or using such water for cooking leads to illnesses and may even cause death.
Contaminated or non-potable water can be treated to turn it into potable or drinking water.