Today... two words, which are related with each other.
Baw, n. non-potable water, usually a great still body of such water.
Spär, n. potable water, water which has undergone treatments to ensure its potability.
So as you may see, baw is not only any non-potable water, but it may also refer to the water in any lake, sea, or Ocean. Whereas spär is not only water that can be drunk, but also it implies that it has been treated to be so. Therefore, while you could drink water from a well or a river, you wouldn't be able to call it spär. Sometimes Tulvanians say baw ispär "potable still water" or bawspär to make the distinction.
This kind of water can be used to mean "a glass of water" as in the example below. But the "water of the sea" would undoubtedly be rendered as baw.