Backwashing of filters
Only granular (sand) filters require backwashing. Regular backwashing of filters in accordance with the manufacturer's specification is essential for proper cleaning, maintenance and operation of pool filters. Swimming pool backwash wastewater consists of all of the pollutants that are filtered from a pool. Most pollutants are introduced into the pool from bathers. Backwash water may be heavily polluted with a wide range of pathogenic micro-organisms and chemicals.
Reuse of backwash water (externally)
Usually the wastewater generated from backwashing is discharged to the sewerage system in accordance with a trade waste agreement with the local sewerage authority. As water is scarce in many areas of Australia, treated backwash water is reused for cleaning and irrigation purposes and, if highly treated, for recycling into the pool and for toilet flushing.
Under no circumstances should backwash wastewater be directly discharged to the environment or to the stormwater system. The wastewater is extremely harmful to the environment and promotes weed growth in natural bushland areas.
The backwash wastewater may be suitable for reuse on parks and gardens or for dust suppression on road works if properly assessed and pre-treated. Untreated and un-disinfected backwash wastewater must never come into direct contact with people.
The reuse of backwash wastewater must be fully assessed and a water reuse plan developed. A health risk assessment should be performed using Environmental Health Risk Assessment - Guidelines for assessing human health risks from environmental hazards (Updated 2012) .
Issues to consider in the health risk assessment include:
- reduction of salinity / total dissolved solids
- potential reuse options
- savings on discharge to trade waste
- costs of reuse
- environmental grants
- treatment / pre-treatment / disinfection
Recycling of swimming pool backwash wastewater
To conserve water, recycling of treated backwash water to top-up swimming pools and spa pools is supported provided the backwash is treated to an acceptable standard and controls are in place to protect public health.
Recycling swimming pool backwash water involves treatment to a suitable standard to allow recycling into the pool. As pool water will be accidentally swallowed, the quality of recycled backwash water should meet the Australian Drinking Water Guidelines (Updated 2012)  and controls need to be in place to protect against system failures. Any deviations from these guidelines should be supported by a health risk assessment.
The National Water Quality Management Strategy, Australian Guidelines for Water Recycling: Managing Health and Environmental Risk (Phase 1)  should be used as a guide. Environmental Health Risk Assessment - Guidelines for assessing human health risks from environmental hazards (Updated 2012)  also includes useful information.
Appendix C of the NSW Ministry of Health, Public Swimming Pools and Spa Pools Advisory Document December 2012 provides an example of some of the components to consider for recycling of swimming pool backwash water based on Australian Guidelines for Water Recycling: Managing Health and Environmental Risk (Phase 1) .
Reverse osmosis is presently the best available technology for the treatment of backwash water for recycling. Pre-treatment using ultra-fine filtration and granular activated carbon may be necessary to prolong the life of the reverse osmosis membrane.
Reverse osmosis has been shown to remove the majority of dissolved contaminants (more than 99.5% dissolved salt and up to 97% of most dissolved organics), and 99.99% of micro-organisms. However because of the high set up, operational and maintenance costs, the cost of recycling backwash may outweigh any benefits. Reverse osmosis should be installed with supporting treatments to greatly enhance its efficiency. The advice of a consultant in designing a recycling plant is essential.
Components to consider in recycling swimming pool backwash water
(Developed for use with Australian Guidelines for Water Recycling: Managing Health and Environmental Risk (Phase 1) (2006)
Element 1: Commitment to responsible use and management of recycled water quality
- Recycled water policy
- Regulatory and formal requirements
- Engaging stakeholder
- Regulatory framework compliance
- Water Quality Guidelines:
- NSW Health. Public Swimming Pool and Spa Pool Advisory Document 2012
- Australian Drinking Water Guidelines
- Health Risk Assessment Guidelines:
- Australian Guidelines for Water Recycling: Managing Health and Environmental Risk (Phase 1), 2006
- Develop a recycled water policy
Element 2: Assessment of the recycled water system
- Identify intended uses and source of recycled water
- Recycled water system analysis
- Hazard identification and risk assessment
- Source of water
- Backwash from swimming pool(s)
- Reverse osmosis
- Ultrafine filtration (UFF) and/or granular activated carbon (GAC) may be recommended
- Intended uses
- Recreational swimming
- Hydrotherapy (possibly immunocompromised clients)
- Learn to swim (infants not toilet trained)
- Exposure routes
- Ingestion (100 mL) - more for infants
- Dermal: disinfection by-product (DBP) - trihalomethanes (THM)
- Inhalation: DBP - THM
- Assessment of water quality data
- Turbidity, pH
- Microbial quality
- Chemical quality (DBP-THMs)
- Water quality indicators: total dissolved solids (TDS) conductivity
- Treated backwash water to be tested prior to reuse
- Microbial hazards
- Chemical hazards
- Hazards from failures
- Control to prevent failures
Element 3: Preventive measures for recycled water management
- Preventive measures and multiple barriers
- Critical control points
- Preventive measures
- Control of bather hygiene, showers prior to pool entry
- Treatment: best available technology (RO, UFF, GAC, ultraviolet [UV])
- Validation of treatment system
- Pipework purple with reuse caution and signage (may be needed)
- Documentation of responsibilities, operational procedures
- Backflow and cross connection prevention
- Controls - monitoring, shutdown upon failure
- Recycled water should be tested prior to reuse, otherwise alternative clean water source should be used
- Failures should be communicated and reported
- Education program for operational staff
- Validation prior to commissioning to ensure that recycled water complies with the standards for drinking water
- On-line monitoring of pool water for TDS, free chlorine and/or oxidation-reduction potential (ORP)
- Determine critical control points
Element 4: Operational procedures and process control
- Documented procedures
- Operational monitoring (auditing of critical limits for TDS/conductivity)
- A contingency plan should be developed to effectively deal with pool contamination events
- Corrective active
Element 5: Verification of recycled water quality and environmental sustainability
Water quality monitoring (turbidity, TDS, DBP, microbial)
- Receiving water monitoring - swimming pool water
- Documentation and reliability
- Annual reporting of water quality monitoring results to Public Health Unit (PHU)
- Short-term evaluation of results
- Corrective action
Element 6: Management of incidents and emergencies
- Potential public health problems should be reported to PHU
- Non-compliance with approval conditions to be reported immediately to PHU
- Incident and emergency response protocol
Element 7: Operator, contractor and end user awareness and training
- Skilled and trained operator
Element 8: Community involvement and awareness
- Community consultation and education
Element 9: Validation, research and development
- Validation of processes
- Design of equipment
- Investigative studies and research monitoring
Element 10: Documentation and reporting
- Management of documentation and records
Element 11: Evaluation and audit
- Long term evaluation of results
- Audit of recycled water quality management
Element 12: Review and continual improvement
- Review by senior management
- Recycled water quality management improvement plan
- Australian Government Department of Health and Ageing, enHealth Council. Environmental Health Risk Assessment - Guidelines for Assessing Human Health Risks From Environmental Hazards. Canberra. Contact the enHealth Secretariat (enHealth.Secretariat@health.gov.au) to request a copy.
- National Health and Medical Research Council (NHMRC), Natural Resource Management Ministerial Council. National Water Quality Management Strategy. Australian Drinking Water Guidelines 2012. Available at http://www.nhmrc.gov.au/guidelines/publications/eh52 (Cited 28 November 2012).
- National Resource Management Ministerial Council; Environment Protection and Heritage Council; Australian Health Ministers Conference. National Water Quality Management Strategy. Australian Guidelines for Water Recycling: Managing Health and Environmental Risks (Phase 1). 2006. Available at http://www.environment.gov.au/water/quality/publications/nwqms-australian-guidelines-water-recycling-managing-health-phase1 (Cited 28 November 2012)
- NSW Ministry of Health. Public Swimming Pool and Spa Pool Advisory Document Sydney: NSW Health, December 2012. Available at http://www.health.nsw.gov.au/environment/Pages/swimming-pool-and-spa-advisory-doc.aspx
For further information in NSW call 1300 066 055 to talk to your local Public Health Unit.