Boil and Let Cool or Let Sit Outside
One completely free method is to boil your tap water, which can easily be done on the stove in any pot, for about 20 minutes. Boiling your tap water will make the chlorine evaporate, because it will bring the chlorine solution in the water to a temperature where it will more quickly turn into a gas. Of course, before drinking the water (or putting it in the fish tank), let it cool to room temperature or put it in the fridge to chill.
Instead of boiling the water you could also let a pot or bucket of uncovered water sit outside in the sun, exposed to UV light, for a long period of time (at least a full 24 hours). This will allow the chlorine to naturally evaporate through off-gassing and UV exposure. If you have an especially big tank of water to dechlorinate, this method may be easier than boiling.
If you chose to naturally evaporate the chlorine, know that the precise amount of time required will depend on a number of factors, including the initial chlorine concentration in the water and the amount of sunlight exposure. Additionally, the deeper and more narrow the container, the longer it will take to dechlorinate. Ideally, you could periodically check the chlorine levels with a small chlorine test kit.
Keep in mind that evaporation (whether naturally or through boiling) is not guaranteed to remove all chloramine, which is sometimes used as an alternative disinfectant to chlorine. This is because chloramine is more resilient and is not turned into vapor as easily as chlorine. So be sure to check what kind of disinfectant your community uses in its tap water.
Adding vitamin C is another good option for removing chlorine or chloramine from tap water, and it is often used to reduce or eliminate chlorine content for large amounts of water like pools and hot tubs or baths.
Of course, this means investing in some Vitamin C powder or tablets. And depending on how much water you need to dechlorinate and hw frequently, the cost can add up.
However, Vitamin C is effective in eliminating chloramine, unlike the sun or boiling options described above. About 45 mg of Vitamin C will dechlorinate 4 litres of water (just over a gallon) treated with chloramine or chlorine.
If your goal in dechlorinating is to end up with the purest water to drink, consider investing in either a carbon filter or a reverse osmosis filter.
Activated carbon filters typically remove organic compounds, chloramines and chlorine from water. Many carbon filters can be directly linked to your tap water supply outside your home or you can also use a pitcher with a drip carbon filter built-in.
Reverse osmosis filters work by removing ions and other particles from your tap water. You can link the reverse osmosis filter directly underneath your sink or where your water supply enters your house.
Because filters can often be attached directly to the water supply in your home, they are usually the most convenient option for dechlorination. Keep in mind, however, all filters will need to be changed or replaced eventually.
Chemical dechlorination agents can be another effective means of reducing chlorine concentrations in your tap water. They are especially popular for fish tanks and dechlorinating water before putting it back in the natural environment like a stream or pond. These products are also called water conditioners or tap water conditioners.
If you need to dechlorinate your fish tank, chemical agents are available at most pet stores.
Know that there are a number of options for those who are looking to dechlorinate their tap water. The best option will depend on the context – what is your ultimate goal in dechlorinating? How much and how often do you plan on dechlorinating? And how much time, money and energy do you want to invest?
Regardless, there will likely be at least one (and possibly, more than one) method of dechlorination that will be a ‘fit’ for your situation.