Watercooling (WC) is the probably the safest long term cooling solution that provides safe low temperatures.
There are method to cool it way beyond what WC can do, but I'd not recommend it; Pelters, phase changers, Liquid Nitrogen, Coolant submerging etc

The sort of temperatures you can expect out of water cooling will be dependant on your WC setup, how many parts you are cooling and your air temperature around the PC, since that is the coldest it will get too.
Usually I'd go for 1 240x120mm Radiator per CPU or GPU needing cooled, so room temperature is the best it will be at.
By the way, some of the best fans for WC and air cooling is Scythe Gentle Typhoon series, noisy, but does the job and you can always use a fan controller to lower the voltage if you need it quiet.

Trying to go significantly below room temperature is not recommended, as you have a lot more to consider in the areas of condensation and other issues if you go below freezing. It can be done, but it's not for those for good for those with more experience in this area of more cooling first.