If it gets cold enough the ice that forms is relatively fresh. Repeated freeze/thaw cycles and slow freezing rates increase the purity and ice on top of sea water is often drinkable water.
You can often tell by the colour how good it is. Clearer is better than greyer.
The effect is strong enough that you can have pools of fresh water form on old ocean ice in the arctic.

Another odd feature of some beaches is that fresh water often sits in a layer just inland from the beach and on top of the salt water layer in the ground. (Ghyben-Herzberg lens)
If the salt water has formed a water table the fresh water floats on top and for every foot it is higher than sea level it will be 40 feet deep. It tends to form a lens shape like most other floating liquids, so it can be thin near the edge but quite deep if it covers much area.
So you might find water if you dig a hole on the land side of the beach, especially if it is sandy.

Another point is you can use the seawater for many things you don't need drinking water for.