Many plants are sensitive to the quality of the water you water them with.
For example, orchids do not like hard water and you must soften tap water with vinegar or use distilled water.
But not with hydroponics: by adding the nutrients, the water is immediately suitable and does not have to softened.
What you should pay attention to, is the temperature of the water: many plants do not like the cold water from the tap and it is therefore better to let the water get to the ambient temperature before using it.
Water that was treated through a water softener based on ion exchange must be avoided though: it usually contains too much salt (NaCl) and this is harmful to plants.
- Water faucet: Alex Anlicker