The relative temperatures of water is of interest, when one thinks about it.

I addressed this in the aqueduct article I posted years ago on the old "The Ancient Vine." The passage in question, followed by the referenced foot notes:

When Agrippa built the Julia in 33, he carried out radical changes on the Tepula. As the name indicates, the water of the Tepula was rather warm and regarded as unpalatable. Modern temperature readings give the temperature of the water at the source as 63° F, which is probably not too far from that of the ancient temperature.[8] Agrippa placed the intake for the Julia about two miles further south, tapping a cooler source, 50° F F, and combined the Tepula with it, abandoning the Tepula's original channel for the rest of the way into the city.[9] Thus, the combined waters were brought in at a temperature of about 53-54° F.[10]

8 Clemens Herschel, Frontinus and the Water Supply of the City of Rome, p. 164; Ashby, p. 160; Van Deman, p. 149.

9 Frontinus, 9; Van Deman, pp. 147-148; Ashby, pp. 159-160.

10 Herschel, p. 164. The question of temperatures may seem trivial, but it is of some importance for consumption, even if it may be more psychological than anything else. As everyone knows, water may be cold to the touch, but not to the palate. For example, a test of the tap water where I live comes up with a temperature of 62-63° F, whereas the water jug kept in my refrigerator is at 38-39° F. This is a marked difference in satisfaction on a hot day. The same tap water temperature is very cold to the touch in the shower, though.*

Now, there is another aspect to this. In the summer of 1973, I was enrolled in an Etruscan archaeology course at the Rome campus of Trinity College of Hartford, CN. Back then, as now, their campus was in half of a convent on the Aventine. The nuns had some interesting ideas on housekeeping. One of these was that it was much easier and efficient to keep the toilets clean in the individual dorm rooms if they had no seats. In short, if you need to sit on the john, you sat on the bare porcelain bowl. Really.

Now, I can personally attest that, on a hot summer day, June through July, at least, sitting down on that nicely cool porcelain can be surprisingly refreshing.

*for the full aqueduct article, go here.