The Deipnosophists (2.16)

But there are some waters which have a good deal of body in them, and are of considerable weight; as that in Trœzen,—for that gives the mouths of those who taste it a feeling of fulness. And the waters near the mines in Pangæum, in winter, weigh ninety-six drachms to half a pint, but in summer they only weigh forty-six. For the cold contracts and condenses it; on which account that which is used in hour-

glasses does not make the hours in winter the same as those in summer, but longer; for the flow is slower on account of the increased density of the water. And he sys that the same is the case in Egypt, though the air there is softer. Brackish water is more earthy, and requires more working; as also does sea-water, the nature of which is warmer, and which is not exposed to the same changes as river-water And there is one salt spring which is of invincible hardness,—I mean that of Arethusa. But as a general rule heavy waters are worse, and so are hard and cold waters, for the same reason; for they are not so easily prepared for use, some because they are very earthy, and some from the excess of cold. But those waters which are quickly warmed are light and wholesome. And in Crannon there is a spring of a gentle warmth, which keeps wine which is mixed with it of the same temperature for two or three days. But flowing waters, and waters from aqueducts, are, as a general rule, better than stagnant ones, being softer because of the collisions to which they are subjected; and on this account water derived from snow appears to be good, because its more drinkable qualities are brought to the surface, and are exposed to the influence of the air; and for the same reason they think it better than rain-water: and on the same ground, too, they prefer water from ice, because it is lighter; and the proof is, that ice is itself lighter than the rest of the water. But very cold water is hard, as being earthy; but that with much body in it, when it is warmed, is susceptible of greater heat, and when it is cold, descends to a more intense cold. And for the same reason water on the mountains is better to drink than water in the plains; for there is in such less admixture of earthy matter. And it is from the earthy particles present that waters vary in colour: at all events, the water of the lake at Babylon is red for some days after it is drawn; and that of the Borysthenes is for some time of a violet or dark colour, although it is unusually thin in quality; and a proof of this is, that at the point where it meets the Hypanis its waters flow above those of the latter while the north winds prevail.