How to Use Soft Water in Hydroponics


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.

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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

Step 5

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.

Step 6

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.

Step 7

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.

Step 8

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

Tips and Warnings

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

Things You'll Need

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


  • Simply Hydroponics and Organics Website: pH
  • Water Quality Association Website: Water Quality
  • North Carolina Cooperative Extension PDF: Growing greenhouse tomatoes in soil and * in soilless media

Who Can Help

  • EPA Website: State Certification Officers for Drinking Water Laboratories
Keywords: hydroponic plants, soft water, controlling pH

About this Author

After 10 years experience in writing, Tracy S. Morris has countless articles and two novels to her credit. Her work has appeared in national magazines and newspapers, including "Ferrets" and "CatFancy," as well as the "Lexington Herald Leader" and "The Tulsa World," and several websites.