Hooking it up to a water supply. Easiest way would be to hook it up to a sink faucet
I'll jump in on the RO/DI water. I have a four stage system, hooked up to an outdoor faucet. My water can, a 20 gal brute is in the kitchen. Both the inline and out line (waste water) go out through a small hole in the window screen. I mounted the unit over the water can. I have to actually go outside, turn on faucet (have a split faucet so have to choose which hose) and set a timer so I don't forget and flood kitchen (like I did today...) I take a length of pvc and insert waste line so water goes into garden until I get an outside waste water barrel to use to water garden.
it's far worth it to get your own. I choose spectrum, got it from Amazon and it has 2 meters to measure in and out numbers as I wanted something good and name brand. Upside is, I make water for household use as well. I looked into buying water from a water store and way too costly and I have no fish store close by. With as many water changes as I've done in my first 7.5 months, well worth it.