Water can make or break your best attempts at great coffee. Because the minerals in water are essential to the extraction process (and having them present in the correct amounts) this is a very important part of coffee brewing! There’s a lot of science and chemistry involved in a simple thing like water and it can become quite a rabbit hole to go down and explore! If making your own water isn’t your thing, I would just recommend to use a product like https://www.crystalgeyserplease.com
Waters to avoid: Softened (It’s too high alkaline / carbonate hardness), Distilled water (No mineral content) or Municipal water that contains Chlorine.
RO, while not ideal (It’s generally too low mineral/TDS) can still be an okay brewing water if you adjust other brewing parameters, ie grind courser or increase the dose.
If you want to make you own water I would recommend that you start here: https://coffeeadastra.com/2018/12/16/water-for-coffee-extraction/ https://www.baristahustle.com/blog/diy-water-recipes-redux/
You will also want to buy this titration kit https://apifishcare.com/product/gh-kh-test-kit It allows you to measure and track the waters/recipes you’re working with. I’d also recommend getting a conductivity TDS meter. They’re cheap and easy method to track total TDS, but not the actual mineral composition.
My current water recipe is: TDS – 74, GH – 85, KH – 60 (I tend to prefer KH between 55 & 60)
Remember to periodically clean any containers / water holding that are used to store water as bacteria can also affect coffee flavors.