Drinking water typically does not provide significant quantities of any essential minerals. For example, the USGS threshold for "hard" water (heavily mineral-laden) is 120 ppm of combined calcium and magnesium carbonates. At that level, drinking the recommended two liters a day would only give you a few percentage points of your required daily intake of elemental calcium and magnesium.

Yes, googling "reverse osmosis demineralized water" provides many options to add minerals back in.

The WHO stated that demineralized water is unsuitable for long term drinking due to the lack of minerals.

Not sure how significant this is or how many minerals you can get from diet instead of water.