Tap water is chlorinated and also depending on where you live can be pretty nasty. I have well water that has ALOT of iron. I have to use a water softener which salt isn't good for plants in excess. Plus I don't think the iron wood be good either. I've heard of people using the water from air conditioning systems, and dehumidifiers. I buy distilled and being I use a gritty mix I go through quite a bit. I will be getting a bin to collect but I also live on a little over ten acres that's mostly wooded and they're are tons of Mosquitos. I really don't want to attract more lol. But a cheaper alternative is those machines that are outside the supermarkets (I forget what they call that water) but that'll work too. I've heard some people take tap water and set it out over night and that's supposed to help but quite frankly there is SO MUCH CRAP in tap water. Yuk! Have you ever poured a glass and looked at all the nasties twirling around In there? All that is going to your plants and builds up and then can cause a decline in them. Hope I've helped. I'm sure others will chime in and be able to tell you what alls in it and such and why it's bad

depends on your local water. See if you can figure out the supplier (local water company) then go to the supplier's website and read their water report on pH, and carbonate content. If the pH is near neutral or very slightly acid, and the particulate content is low, and they use chlorine instead of chloramines, you can just let a watering pot sit for a couple of days to get rid of most of the chlorine and water with that. I use distilled on my orchids and they really appreciate it. Cactus like it also. Succulents like crassula, agave, aloe--they are not fussy.

On the website for the water supplier closest to my college, it didn't give a pH level, but it did list some compounds that humans probably should not be taking in their water, never mind my plants. (Something that smells like paint thinner...)

Another question: I think I might be overwatering my cactus and succulents. Should I be watering them until water comes out of the bottom of the pot, or just a little bit of water to wet the soil?

I definitely don't risk it and use tap, I buy distilled water in 4L bottles from local pharmacy, they're quite cheap and I don't have that many plants so it's definitely very affordable and worth it. I put them into 2 bottles and one has some diluted fertilizer and one is just pure water.
I try to collect rain water once in awhile but sometimes bugs climb in and sometimes it just collects a lot of unwanted dusts/garbage too so I don't find it very doable in my case

On your question about watering until water comes out drain holes: typically that's what they need, BUT some soils hinder this from happening. Store bought soil straight out of a bag., holds too much water and at the VERY least should half perlite mixed with it. If you go to the search bar on this forum and search Al's gritty mix it will explain ALIT about water retention in soil and such. There's some great recipes for mixes that succulents THRIVE In. I made the switch to the gritty mix and imy plants LOVE it! It allows you to water your plants correctly WITHOUT the fear of rot. Hope this helps you!

LilBit, there is many ways you can avoid mosquitoes - all you need is to put a mesh :(like window screen) over the opening of the rain barrel (or whatever you collect water into). It will also keep leaves etc. out of the water. You could also use small pieces of 'mosquito doughnut'. I use it in bird bath. Or even tiny bit of oil (cooking oil), it will create film on surface.
I use to have very small lot (just 45x125feet) & had at least 3 water barrels at any time. Used that to water garden & pots.
Now I have well ('free water'), but still collect; at the moment, there are 6 water barrels + one large white storage container I think it's 275gal.
And I always use water from dehumidifier (if using it).
Having all that space, all the free water...Rina

Thanks Rina!! I appreciate it! Now that I'm reading this, I'm like "duh" "and hitting my head like in the v8 commercials!! Lol! Thanks for the advise! ðÂÂÂ