Soft water, in the most basic form, is water that has had salt added to it. There are some benefits of softened water, but using soft water on plants can be harmful to them. If used to water plants, soft water can make it hard for the plants to grow and limit the availability of nutrients. It can also leave salt deposits in the soil that can build up and prevent anything from growing. There are a few reasons to use soft water in the home, however, including the prevention of pipe blockages from mineral buildup.
Buildup of calcium in showers may also be prevented with softened water. The treated water does not remove harmful substances such as lead. It can therefore cause other problems if used for cooking or drinking, and should not be used with plants either. The salt, or sodium chloride, prevents water from being absorbed by a plant. Using soft water on plants at home or in the garden can dehydrate them; not enough water will be absorbed for sufficient growth, or the plants could die.
Calcium can be detrimental to plumbing systems, but is an essential nutrient for plants and gardens. Using soft water on plants can also wash away calcium and other substances that are beneficial. Usually, not enough nutrition is available if softened water is used for watering plants. The salt deposits can remain in the soil, and even spread when it rains. Whole gardens and the land around them can become unsuitable for growing plants at all.
For anyone who needs to use soft water on plants, it is important to test the nutrient level of the soil often. There are soil testers than can help monitor nutrient levels. Calcium and other nutrients will have to be added on a more regular basis as well. It also helps to dilute the soft water; adding rain water or mineral-filled fluid can help replace the nutritional substances in the soil.
The acidity of soft water makes it suitable only for plants that grow where the soil is acidic. These include tomatoes, azaleas, roses, and blueberries. Otherwise, soft water on plants can be detrimental to their ability to thrive and could possibly kill the entire garden. Soft water is also not the best option for use in drinking water, infant formula, or cooking because it can contain dangerous heavy metals. It is, however, fine for use with laundry or in equipment such as steam irons and car batteries.