Since you will be practicing the art and science of "water gardening", it is a wise idea to know what your local water contains.
Contact your local water company and ask for their water quality analysis.
If your water comes from a well, you will most likely have to send it out to a lab for analysis on your own.
The most important factor affecting water quality is its relative "hardness" or "softness".
Hand water means that there is a lot of dissolved mineral content, primarily calcium carbonate, which is often seen as scale on hot water pipes.
Soft water is generally very pure or low in dissolved solids. Distilled (or deionized ) water, or water that has been through a reverse osmosis filter, are all considered soft. Most commercially available hydroponic nutrients are made for soft water. However, if you have hard water, there are some nutrient products made for hard water as well.