Clean water is essential for human survival. We could survive for up to several weeks without food, but only a few days without water.  However, water is often a carrier of many pathogens, even the water that comes out of your faucet. This is why many homes today will need a  water filter  to make the water being drunk clean and potable. Without a water filter, even the water from your city of municipal water system might be contaminated. It will be best in all cases to be prudent as it is your very health that is at stake.