Apax Lab Wassermineralien-Set

You can make your own water to brew with, purchasing bulk minerals to brew with are cheap and accessible online.
That being said this is the hardest approach to go about making brew water for coffee.

Aquacode, Third Wave, Apax Lab are all pre made profiles of water minerals.
This is the easiest option to make great tasting coffee, simply add your minerals into water and use this to brew coffee with.

To test the effects that certain minerals have on coffee you can brew up a batch of coffee, pour this into multiple cups and add different minerals to each sample to taste the difference.