The Effects of Filtered Water on Plants

Minerals

• Unfiltered tap water contains iron, calcium, magnesium, phosphorus and potassium needed for healthy plant growth. Modern methods of filtering or distilling water removes these vital nutrients. If you are growing in nutrient-rich potting soil, watering with filtered water will not harm plants. Plants extract minerals from the soil. Plants grown hydroponically in filtered water will require mineral supplementation.

Tap Water Versus Filtered Water

• If you are in doubt about the quality of your source of drinking water, take a sample to your local county extension office for testing. Request a test that identifies salts, pH levels, nutrients, fluoride and chlorine levels. Fluoride and chlorine can be detrimental to plant health. If your water is the cause of poor plant growth, you may wish to water with filtered or distilled water and supplement nutrition with an organic liquid fertilizer. When applying fertilizer to houseplants, follow the manufacturer's label instructions, diluting the mixture to half-strength with filtered water.

Sodium

• Both rural wells and city water systems can have water that is healthy for humans but that contains excessive salts that plants cannot tolerate. Look for a white, filmy crust on the top of the soil of your houseplants. The white crust is indicative of salt build-up. Flush your plants with several rinses of distilled water or replant the ailing plant in fresh potting soil. If your tap water is high in sodium, watering with filtered or distilled water is the preferred method.

Fluoride

• Many municipal water systems add fluoride to city drinking water. Fluoride is effective for preventing cavities in humans, but many plants are sensitive to fluoride and do not respond well when continually watered with fluoride-treated water. Palms, ferns, spider plants and dracaenas are especially sensitive. Savvy gardeners allow water to sit in an open container for 24 hours prior to use. The wait period will allow some of the chemicals in the water to evaporate.