Calgary has perfectly fine water IMO and I don't consider needing to fight it. Someone wants crappy water go to a 3rd world country. Hard yes but quite suited for aquatic life. Like anything find what works with what you have or be prepared to change the water to suit what tank stock you want.
Calgary water is perfect for many FW fishies and ideal for Cichlids. Their home environment water is almost identical to our water. For water changes on my FW tank, I use straight from the tap ie not treated. However I don't keep sensitive fish or sensitive shrimp. I do keep a fully planted 75gal Cherry shrimp tank and it's flourishing both plant and shrimp. I have used basic dechlorinators in the past but it's a waste of $ for what I have. If you or anyone have any FW questions, I'd be happy to answer anything for you.
The other side of the coin, SW...you must use proper treated water such as RO water since the ocean and tap water are very very different but this is basic knowledge.
I had purchased a 6 stage RO unit for both for drinking and for the SW tank. The product link which was given for MaxWater was where I bought my unit.
For the point on rainwater this typically isn't recommended even though yes it's straight from the sky. The problem is where it lands (ie roof) isn't always nice and clean.