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How to Use Soft Water in Hydroponics

By Tracy Morris ; Updated September 21, 2017

Hydroponics is the process of growing plants without soil. The plants can be grown directly in a liquid mixture of nutrients and water, or in a soilless mixture of perlite or peat moss that has been saturated with the liquid solution. However, since plants are grown without soil, they are more sensitive to all minerals present in the liquid solution. If tap water is used to mix the nutrient solution, it may contain minerals such as calcium and lime. Water with these minerals is known as hard water. Using water without these minerals, known as soft water, allows you to control the contents of the nutrient solution in your plants more thoroughly.

Examine your home for evidence that your tap water may be hard water. Evidence of hard water includes white spots, which are calcium deposits, on your shower, around your tap or in your coffee maker.

Drop a few drops of liquid soap into a glass of water. If your water is soft, the water will form suds. If you have hard water, the soap will not form suds.

Call your city or community water supplier to inquire if your water is hard. Or, if you have a private well, contact an EPA certified laboratory to have a sample of your water tested. If you determine that your water is hard, you can take steps to soften it.

Mix hard water with baking soda at a rate of 1 tablespoon per 5 gallons of water to soften the water.

Mix the softened water with a pre-mixed hydroponic nutrient solution formulated for soft water. Hydroponic nutrient solutions are typically low in nitrogen and high in phosphorous.

Test the pH of the nutrient solution with a pH tester. You may purchase a pH tester from a commercial greenhouse. A pH of 7 is neutral. A higher number indicates an alkaline nutrient solution, while a lower pH indicates an acidic nutrient solution.

Raise the pH of an acidic solution by adding a small amount of potassium hydroxide to the mixture. Lower the pH by adding phosphoric acid. Both of these substances are available through the same hydroponic supply stores that furnish nutrient solutions.

Add the mixed nutrient solution and soft water to the reservoir chamber of your hydroponic plant’s pot.


Things You Will Need

  • Tap water
  • Liquid soap
  • Baking soda
  • pH testing kit
  • Nutrient solution
  • Potassium hydroxide
  • Phosphoric acid


  • When administering the soap test to your water, make sure that you are using liquid soap, and not liquid detergent. Detergent is formulated to create suds even in hard water. Soap is not.
  • PH testers work by testing the acidity or alkaline level of a liquid solution. To test the pH, place a small amount of the liquid in the pH testing chamber. Then drop the testing solution into the chamber. The testing solution will change the tint of the liquid based on the pH level of the water.


  • When mixing the nutrient solution or handling acid or potassium hydroxide, it is wise to wear protective clothing, goggles, gloves and a breathing mask.

About the Author


Tracy Morris has been a freelance writer since 2000. She has published novels and numerous online articles. Her work has appeared in national magazines and newspapers including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World." She holds a Bachelor of Arts in journalism from the University of Arkansas.