Why was the water from some aqueducts that fed the water to ancient Roman fountains(nasoni) cold?
This drifts into a science Stack Exchange question somewhat, but consider the following:
- Until the advent of PVC pipes, stone aqueducts would have insulated the original (cool) temperature better than exposed metal piping. Unexposed piping would have been about equivalent to stone depending on ground temperature.
- If I recall correctly Roman aqueducts didn't have large urban reservoirs per se; so the effect of continuously flowing water would cool down the drinking supply before it reached the fountain. In the case of open air aqueducts the more energetic water molecules could have escaped the system entirely.
Water mainly came via the Avens river Nar (that goes into Tiber) from lacus velinus near Reate. Its water came from mountains. Marius Curius Dentatus has drained the waters of the lake into the river Nar. In doing so, he created the marmore waterfalls:
The Marmore Falls, extolled during the centuries for its beauty, appears like a roaming water column distributed on three drops. Wrapping the flora in a cloud of white foam , cover a different in high of 165 metres. The scenery disclosed to the visitors eyes is the work of men made since centuries, from the Roman period, tried to canalize the waters of the Velino river to fall the into the Nera river.
Its history began in 271BC when the Roman consul Curio Dentato made a reclaimed work in the plain of Rieti realizing a canal of beyond two kilometers up the cliff of Marmore.
The lake is now known as Lago Piè di luco
"Rivers and the Power of Ancient Rome" By J. B. Campbell
Dictionary of Greek and Roman Geography: Iabadius-Zymethus by Sir William Smith