Upvote:0
Roman aqueducts didn't freeze largely because they were in Italy. It's quite warm there, check climate data for Rome and other cities on wikipedia.
Upvote:6
Aqueducts did, in some cases, freeze over. Aqueducts were built underground in the northern provinces to even out the temperatures over the day, and this helped a bit.
http://staff.civil.uq.edu.au/h.chanson/rom_aq.html http://www.eng-tips.com/viewthread.cfm?qid=262678
Flow rates are 5 to 70 L/s on modern models of Roman dropshafts. However, you can't prevent water from freezing over long distances just by increasing the flow rate. Presumably there was no running water if it became too cold.