Plain tap water is often used to water the garden and for houseplants, but in virtually all areas of the United States, tap water has additives such as fluoride and chlorine. In January 2011, the United States Department of Health and Human Services announced plans to lower requirements for fluoride levels in tap water, but not for chlorine. Gardeners who prefer to use water that has neither fluoride nor chlorine may use alkaline water for both indoor and outdoor plants.
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Alkaline or ion water contains no fluoride or chlorine and has a low acidity level. Ions are salts, and some salts are bad for plants. Knowing what is in your water will help you determine what kind of fertilizer your plants need as well as whether the plants need to be watered with alkaline water.
Alkaline water does not introduce fluoride and chlorine into your plant, so if you worry that these additives may harm your plants or transfer chemicals to you when you eat vegetables from your garden, you may choose to water the plants with alkaline water. Some houseplants, like dracaena and spider plant, can be injured by fluoride in tap water. Chloride (from chlorine) can be toxic to some plants in high concentrations, causing leaf burn. A chloride level below 70 parts per million is considered safe for all plants.
Alkaline water is difficult to acidify and will eventually turn the soil more basic -- lower its acidity. Acid-loving plants such as blueberries and azaleas may starve to death as alkaline water turns the soil more basic and removes iron, manganese and other nutrients the plants need.
If you water your plants regularly with alkaline water, add a fertilizer rich in iron and manganese. You may also need to regularly add sulfur, ammonium sulfate, di-ammonium phosphate, mono-ammonium phosphate, urea or another acid-building compound to restore the plant's soil to its proper acidity level.
Alkaline Water at Home
You can easily make your own alkaline water from regular tap water. Simply fill a container with tap water and let it sit for two or three days, boil the water and let it cool or add baking soda to regular tap water to raise the pH level. The higher the pH, the more alkaline the water. A simple pH test kit, widely available for swimming pools and aquariums, will show if your water has a pH above 7.0, which is the range for alkaline water. Amassing large enough amounts of alkaline water to irrigate a lawn or large garden plot may not be practical. You can use rain barrels to gather untreated water in larger quantities for your garden.