Plants not only need water for growth, but also to reproduce and accomplish photosynthesis. Have you ever wondered why your plants' leaves started to yellow or drop? It may be that high levels of certain vitamins in your tap water is the cause, such as chlorine. In large amounts, a handful of vitamins can be harmful to your house plants, and you may want to consider switching to distilled or rain water.
Too much salt presents a problem for plants, as it actually dries out the soil and roots. Soft water has the highest content of sodium, since vitamins such as dissolved calcium are added to hard water to make it soft. When water has too much sodium, plants also can't absorb water, resulting in leaf and plant burn. You can recognize these symptoms if the plant has brown, dried-out leaves.
Fluoride is a vitamin in water that humans are used to and need for dental hygiene. In low levels, fluoride is not harmful to plants, but if there are high levels, it can damage a plant significantly. Symptoms of too much fluoride in plants will cause sores on plant leaves and signs of burning around the edges. Too much fluoride stunts chlorophyll so photosynthesis doesn't fully complete. The final result if not taken care of is that the plant will have stunted growth.
Humans are familiar with chloride in water softeners. The micronutrient chloride is essential to aiding a plant's metabolism, but like the other vitamins, it is harmful to plants in high levels. If the levels of chloride are too high, plants react in a manner similar to that of high contents of sodium with leaf burn and dropping. The plant can't absorb enough water and has stunted growth.