Not too sure about temperature control, but I've been using the following for keeping my in-house pond stocked with water (picture brightened in PS a bit so you can see better):
It keeps it at the level the water sensor is located all the time by utilizing water duplication techniques and some automation. Super useful, and a really fun entry into practical wiring for myself personally. Takes a few buckets to get started initially, but my ponds are ~ 300 blocks (for fishing) and it filled them in no time, with zero effort on my part after the initial water 'seed'.
The design could be much more compact depending on your needs, but that's the general wiring flow for it. The whole thing is automatic, so you don't need pressure plates, switches, bird engines, or anything similar. Just set it up and you'll never have to manually do anything with it again.
If you want to avoid wiring you could always setup a stair-style duplication method using rain water run off. I had initially designed my base to collect and dupe rain water that way, but that just wasn't reliable enough during dry spells... at least for fishing. For alchemy it'd probably be more than enough to tide you over between seasons.
**EDIT**
Something else to consider: make a sink. I'm not sure of all the details of alchemy (I never bother with it), but if you just need to make bottled water (rather than having access to actual water blocks/buckets) the sink is invaluable as a source of infinite crafting water. I personally prefer ponds over crafting stations, but a sink is definitely a far easier and cheaper solution.