What are some pros and cons from of the following water sources?

Question

Rain/snow

Tap water

Water from the dehumidifier

Distilled water

Answer 1

Rain/snow - falls through the atmosphere and picks up pollutants (it's not only "acid rain" but acid precipitation, which includes snow, hail, sleet, and fog); may only be available seasonally

tapwater - probably the best - it may contain some chlorine (will dissipate in 24 hrs) or chloramine (needs to be treated chemically), possibly some metals, but most water conditioners will neutralize these; it may contain small amounts of nitrate or phosphate (may be a problem or not depending on the amount); also contains varying amounts (depending on where you live) of beneficial elements (calcium, magnesiun) that can be used by your fish

Dehumidifier - is essentially distilled water (no beneficial elements), but may also contain spores of algae (look at what the bottom looks like in a few months if you don't clean it); may also contain bacteria

distilled water - to get absolutely pure distilled water you have to buy it (think $$$), plus it has all beneficial elements removed

Another possibility you don't list:

reverse osmosis water - better than distilled, it has nitrate and phosphate removed (which may be in some areas' tapwater), but also has some, but not all beneficial elements removed; this si a good option for adding TO tapwater if yours has an unusually high mineral content (hard water)

My personal ranking from best to worst:

1) tapwater with conditioner
2) reverse osmosis
3) distilled (as long as combined with tapwater)
3) 100% distilled, rain/snow, dehumidifier

Answer 2

Rain or snow water have a very low PH and may have atmospheric pollution. Also, it's hard to control the temperature.

Tap water may have chlorine or chloramine as well as heavy metal in it, but it's easiest to control the temperature and most standard water conditioners are manufactured to take care of the chlorine, chloramine and heavy metals in tap water.

Water from the dehumidifier is basically slow boiled water and has a low oxygen content without the basic minerals and nutrients that are needed by fish and aquarium plants.

Distilled water has a low oxygen content and is stripped of all minerals and nutrients. It's basically processed so that it won't support bacterial life and you need water that will support life in your aquarium.