In most cases, you should not run a hydroponic system on tap or well water. They can contain things that are harmful to plants. Municipal water is treated with things like chlorine and chloramine.
These are added to kill certain bacteria and microbes in order to reduce or prevent spreading diseases like cholera, dysentery, jaundice, typhoid. Unfortunately they are harmful to the plants.
City water or water from a well can contain concentrations of nutrients, minerals, heavy metals, salts, or other things that can harm marijuana plants, and the people that ingest them.
To be safe, concerned growers have a reverse osmosis water filter or they purchase reverse osmosis or distilled water at a grocery, or similar store that stocks them.
Both reverse osmosis and distilled water production methods are capable of eliminating at least 90% of any impurities. You can measure how pure the water you have is with an EC or TDS meter. The closer the reading is to 0, the purer the water.
Before adding nutrients, the water you use should be as close to 0 as possible. That way you know there is nothing but the optimal quantity of nutrient you add being supplied to the plant via the nutrient solution.
Part 01) See the full hydroponic marijuana nutrient article here.
Part 02) Nutrients and hydroponic marijuana introduction here.
Part 03) Water and hydroponic nutrients here.
Part 04) Preparing hydroponic nutrients here.
Part 05) Measuring hydroponic nutrient solution - EC, TDS, PPM here.
Part 06) Hydroponic nutrient strength here.
Part 07) Hydroponic nutrient solution temperature here.
Part 08) Flushing or leeching hydroponic nutrient here.
Part 09) Amount of water for hydroponic marijuana plants here.
Part 10) Hydroponic nutrient list of materials here.