Generally, you need to take a few fairly simple measures to make your tap water safe for your fish before you add it to their tank or pond.
This is because:
- The temperature of the tap water is likely to be quite different from the temperature in your tank or pond
- Tap water may contain traces of metals that are harmless to us but can damage your fish
- Tap water contains a small amount of chlorine to safeguard our health, which can be harmful to your fish
- The acidity of the tap water is likely to be different than the water in your tank or pond
Check with a local pet store to determine if you need to dechlorinate your water or for other precautions you may need based on your household plumbing and variety of fish.