The amount of water evaporated is going to be effected by many different things like: water temp v. ambient temp, relative humidity and so on. If you put your pump as low as possible in the res it will offer more headway against evaporation. Hooking up to the plumbing for a sink, shower, toilet, washer, etc is not difficult to do. One small hole through a wall can be all that's really needed to run a line of 1/4" ID ice maker tubing to a float valve. Odds are you have incoming water in the next room....there's the source. Holes through drywall are easily fixed.

There are ways to setup a 2-liter bottle, gallon jug, 5gal bucket for short-term auto-refill.....