The Deipnosophists (2.25)

But one ought to avoid thick perfumes, and to drink water which is thin and transparent, and which in respect of weight is light, and which has no earthy particles in it. And that water is best which is of a moderate heat or coldness, and which, when poured into a brazen or silver vessel, does not produce a blackish sediment. Hippocrates says,

Water which is easily warmed or easily chilled is always lighter.

But that water is bad which takes a long time to boil vegetables; and so too is water full of nitre, or brackish. And in his book upon Waters, Hippocrates calls good water drinkable; but stagnant water he calls bad, such as that from ponds or marshes. And most spring-water is rather hard. But Erasistratus says that some people test water by weight, and that is a most stupid proceeding.

For just look,

says he,

if men compare the water from the fountain Amphiaraus with that from the Eretrian spring, though one of them is good and the other bad, there is absolutely no difference in their respective weights.

And Hippocrates, in his book on Places, says that those waters are the best which flow from high ground, and from dry hills,

for they are white, and sweet, and are able to bear very little wine, and are warm in winter and cold in summer.

And he praises those most, the springs of which break towards the east, and especially towards the north-east, for they must inevitably be clear, and fragrant, and light. Diodes says that water is good for the digestion, and not apt to cause flatulency, that it is moderately cooling, and good for the eyes, and that it has no tendency to make the head feel heavy, and that it adds vigour to the mind and body. And Praxagoras says the same; and he also praises rain-water. But Euenor praises water from cisterns, and says that the best is that from the cistern of Amphiaraus, when compared with that from the fountain in Eretria.