Water softeners are useful for providing balanced water to a household. With regard to gardening, though, the effects of water softener on plants can be quite damaging. When a water softener is present in a residence, the best advice is to simply turn off the water softener when watering indoor and outdoor plants.
The salt added by water softeners is very hard on potted plants. In fact, most experts agree that potted plants should not be watered with water softeners because of the impact of salt damage to the roots. The reason water softener damage is more severe with potted plants is because of their limited soil, and, in many cases, limited exposure to rain water.
Water from a softener system has a dual effect on the soil of vegetable gardens. It builds up in the soil and can change the overall texture, making mineral absorption more difficult for the plants. It also changes the pH of the soil to become more acidic over time. Soil that is acidic is less able to hold certain nutrients, including phosphorus, which most plants require for efficient food production.
Ponds and Lakes
Never use water softener water to fill garden ponds. Salt water is extremely harmful to pond fish and can stunt the growth of algae in the water. Freshwater aquatic plants are also adversely affected by the salt water, as they cannot efficiently absorb it for use in food production.