Swimming pools, spa pools and hydrotherapy pools should not be topped up during a boil water alert.

If top up can not be delayed, hyperchlorination should be carried out to minimise an increased risk of infection from Cryptosporidium or Giardia.

Topping up swimming pools

When swimming pools, spa pools and hydrotherapy pools are topped up:

  • the process should be undertaken at night
  • adjust pH to 7.5 and hyperchlorinate the entire pool to achieve 3 log reduction of Cryptosporidium, this can be achieved by adding free chlorine to obtain a residual of 20 mg/L for 13 hours, or 10 mg/L for 26 hours
  •  NSW guidelines for public swimming pools and spa pools draft Aug 2022
  • free chlorine should be below 5 mg/L before swimming


Swimming pool filtration systems should then be allowed to run continuously for seven pool turnovers. One turnover is when the complete volume of pool water has passed through the filter once.

Filter backwashing should be undertaken frequently and regularly.


Free chlorine levels should be maintained at greater then the minimum recommended levels at all times (>2 mg/L for indoor pools; >1 mg/L for outdoor pools).

Precautions during a Boil Water Alert

Current as at: Monday 21 March 2022
Contact page owner: Environmental Health