Can I use tap water in a wildlife pond?

Use rainwater where possible. Tap water can add nutrients that encourage algae, so it should not be the routine first choice for filling or topping up a wildlife pond.

The Natural History Museum says leaving tap water outside for one or two days can allow chlorine to dissipate, but the nutrients remain. That means a bucket left standing is not the same as rainwater. Freshwater Habitats Trust says a drying wildlife pond can often be left to follow its natural cycle, or topped up with water from a water butt if you choose to intervene.

Fish change the risk. The RHS advises topping up a fish pond if its level falls significantly and, if mains water must be used, adding small quantities so the temperature does not change suddenly. Follow any treatment product and fish-system instructions exactly.

Do not assume every falling water level is harmless. Mark the level, switch off waterfalls if safe to do so, and use the leak guide if the fall continues beyond weather-related evaporation.

Make rainwater the easy option

Place a covered water butt where roof water can be collected and reached with a watering can. Keep its overflow and any connection arranged so the pond cannot backflow into the building drainage. Add water gently near a planted edge rather than disturbing bottom silt. If only tap water is available and the pond contains fish, follow the current advice for that fish system and treatment product; do not guess a dose. For a wildlife pond, first ask whether a lower summer level is actually a problem.

Sources

• Natural History Museum: garden pond questions — accessed 14 November 2026.
• RHS: pond care — accessed 14 November 2026.

More from Pond Setup Guide

Read topping up a pond and the first weeks of a new pond. Rainwater and dechlorinator are defined in the pond glossary.