Water is necessary for plants to maintain a healthy nutrient balance. The type of water used can influence health factors. Humans need food to survive, but often the food they consume is not very healthy and can cause imbalance. It is the same with plants. Tap water is often used for plants, even though it can contain harmful substances for them.
Tap water contains several chemicals that can be harmful. Fluoride was added to city drinking water back in the mid 1900s when it was found that some local water contributed to mottled, brownish teeth. At that time there was an issue with bad teeth and the addition to fluoride helped humans to keep healthy teeth. It did not do as well for plants.
Chlorine is another chemical added to city tap water. It is used as a disinfectant to prevent typhoid, cholera and dysentery. Chlorine has some adverse affect on some plants.
Salt is found in most waters, especially when water softeners are used. In a water softening system the water runs through salt before it comes out of the tap. Too much salt is a detriment to many different plants.
Levels of pH
All substances in tap water contribute to the pH level of the soil around the plant. The pH level is the measure of soil acidity or alkalinity. Substances in tap water can make the soil very alkaline and unsuitable for most plants.
An indication of a chemical imbalance shows when the tips and edges of the leaves turn yellow then brown and and go limp or dry. Growth of a plant can be stunted by chemicals in the water. An abundance of salt in tap water will produce a white crust on the soil or around the inside of the pot.
Let tap water set for 24 hours or more before using for plants. Some chemicals will dissipate. Also, the water will be room temperature, which will not shock or surprise the plants. Rain water or distilled water can also be used. Water that goes through a filtration system is suitable for plants.
Some plants are more sensitive to the substances in tap water than others. Outdoor plants that show signs of imbalance when using tap water are azaleas, gardenias and camellias. Indoor plants have an extra disadvantage. They are primarily watered with tap water unless they are placed outside in the summer. The most susceptible indoor plants are dracaenas, palms and spider plants.