Chlorine is a poisonous, corrosive gas that does not occur naturally. It is highly soluble in water and easily absorbed by plants. It is routinely added to municipal water supplies to kill bacteria, thereby preventing the spread of water-borne diseases. High levels of chlorine in tap water can damage your plants, some of which are more sensitive to the chemical than others. Leaves will yellow, and in extreme cases plants might defoliate. Chlorine also kills beneficial organisms living in soil. There are multitudes of devices and gadgets retailed for removing chlorine from tap water. You can buy a filter that attaches to your garden hose. Or you can spend a fortune for a system to treat all the water that enters your home, if you like. However, you can spend little or nothing to easily dechlorinate tap water water for your garden plants.
Fill a kettle or large pot with tap water. Bring to a rolling boil over high heat. Turn the heat down to conserve energy, but keep the water boiling for 20 minutes. Cool to room temperature before using it to water your plants.
Pour tap water into containers with wide openings if you'd rather not waste the energy required for boiling it. The chlorine gas will evaporate from the water in 24 to 48 hours. A wider opening will allow a larger area of the water's surface to be exposed to the atmosphere, which means the gas will dissipate more quickly.
Fill 1-gallon or 5-gallon containers with tap water if you're in a hurry, or if you need to dechlorinate a large volume of it. Add commercial dechlorinator according to the packaging instructions. Typically, the manufacturer's recommendations are given for treating water by the gallon. This will neutralize the chlorine on contact, and the water can be used immediately for your plants.