You can use tap water to fill your koi pond, but it requires careful treatment before introducing it to your fish. Most tap water contains chlorine or chloramines, chemicals used to make water safe for drinking but harmful to koi. These chemicals can damage the fish’s gills and skin, so it’s important to remove them using a water conditioner specifically designed for ponds.
Letting the water sit for a day or two can help chlorine evaporate, but chloramines are more stable and usually require a chemical neutralizer. Testing the water for pH, ammonia, and other parameters after treatment ensures it is safe for your koi. The temperature of the tap water should also be close to the pond’s existing water to avoid shocking the fish. If possible, fill the pond slowly to allow time for the water chemistry to stabilize.
