Because the water supply is the source of life for your plants, quality is important. All plants rely on their ability to uptake water freely. Between 80 and 98 percent of this uptake is required for transpiration (loosely compared to perspiration in animals), which allows the plant to produce and somewhat control its immediate microclimate. Plants also need clean, uncontaminated water to produce their own healthy food supply.
The water you use in your hydroponic system needs to be pure. It is always a good idea to test your water source before adding nutrients so you aren’t adding an element that is already present. In small systems, it would be wise to use distilled water.
If you are starting a larger hydroponic operation, it would be a good idea to have a water analysis completed. Factors such as sodium chloride (NaCl, or salt) content and hardness will be of great use to growers. Also, groundwater can have elements normally not present in conditioned water. A key piece of advice: Get to know your water!