Stainless steel 316 or 316L is suitable for 20°C, on shore conditions and not close to the sea. These values are for potable water.
But water is not water, you can have brackish water, sea water, water from a well etc. Temperature and place of use is also important.
On the Northsea, you can use duplex (sea water temperature up to 20°). In the Persian Gulf you have to use Super Duplex (sea water temperature from 20 upto 34°C).