Swimming pools and spas
Swimming pools and spas are perfect for enjoying the outdoors with family and friends but it’s important to maintain good pool and spa hygiene, especially during hot weather or when the water temperature is warmer than 25 °C.
Water-borne amoebae and bacteria can pose a serious health risk, so it is vital that you keep the water in your pool or spa clean and safe by following good water treatment procedures.
Filtration and disinfection are the keys to knowing your family and friends can swim safely.
Good filtration will rid your pool of dirt, debris and other suspended material.
Common types of filters include:
- sand filters
- cartridge filters
Always ensure the filtration system is operating when there are swimmers in the pool or spa.
The filter system should completely filter all pool water within 6 to 8 hours and remain running for at least one hour after the last person gets out.
Spa filter systems usually take 15 minutes to completely filter all spa water. They should also run for an additional 1 hour before and 1 hour after spa use.
Spas should be emptied every 4 weeks, then cleaned and sanitised and then refilled with scheme drinking water and run for an hour before re-using.
Wading pools should be emptied after each use and the shell sanitised, as leaving the water in the pool provides the perfect environment for harmful amoeba to grow.
As the filter operates, dirt will build up inside and clog the filters. Filters need regular cleaning to operate at maximum efficiency.
Many filter systems have a built-in pressure gauge that will display the pressure level inside the filter. Increasing pressure levels indicate the filter is becoming dirty and will need cleaning.
Systems without pressure gauges need to be cleaned whenever the flow of water from the filter back into the pool or spa decreases noticeably.
Sand and glass filters are generally cleaned by backwashing (sending the water in the reverse direction through the filter). Cartridge filters require the cartridge to be taken out of the filter and cleaned manually.
All filters should be cleaned in accordance with the manufacturer’s instructions.
To prevent the spread of infection, you will need to add a chemical to the water that will rapidly destroy any harmful microorganisms or chemical pollutants in the water but not harm people.
Chemical disinfection processes in pools usually involve chlorine. Chlorine is the most effective chemical that can be used safely in a swimming pool or spa to remove organic and human wastes.
The available chlorine that is not bound to wastes is called free or available chlorine and the chlorine chemically combined with wastes is known as combined chlorine.
Total chlorine is the sum of free chlorine and combined chlorine.
Types of chlorine
Chlorine is available as:
- a liquid (sodium hypochlorite)
- powder or tablet form (calcium hypochlorite).
Both of these forms provide only chlorine to disinfect the water.
Chlorine is also available as a mixture of chlorine and cyanuric acid as:
- a powder – dichlor (sodium-dichloro-isocyanuric acid)
- a tablet, stick or cartridge form – trichlor (trichloro-isocyanuric acid).
These two chemicals add a mixture of both chlorine and isocyanuric acid (called stabiliser) to the water. The function of a stabiliser is discussed below.
Salt water chlorination
Salt water chlorination is the most common method used to disinfect home swimming pools in Western Australia.
How it works
Salt water chlorination systems produce chlorine by passing an electric current through water containing salt, via special electrodes.
Some domestic salt water chlorinators may not produce sufficient chlorine to maintain the level required in the water during periods of heavy usage. A pool will turn a milky colour if overused and cannot be used safely until the water is clear.
During hot weather, pools and spas using salt water chlorination will need to be checked more frequently and extra chlorine added if necessary.
Salt water chlorinators are susceptible to producing a build-up of white-coloured scale on the electrodes, particularly if the water contains high levels of calcium.
Scale can reduce the efficiency of the system to produce chlorine, so salt water chlorinators need to be cleaned manually on a regular basis (as recommended by the manufacturer).
Many modern salt water chlorinators include self-cleaning functions that reduce the need for manual cleaning.
Stabiliser (isocyanuric acid)
Ultraviolet rays in sunlight rapidly break down chlorine in the water. This may mean you will need to use more chlorine to disinfect your pool or spa.
Adding stabiliser (as isocyanuric acid, or as dichlor or trichlor) to the water in outdoor pools will shield chlorine from the ultraviolet light, significantly reducing the amount of chlorine you will need. Stabiliser is not recommended for use in spas or any indoor pool.
Stabilisers should be used carefully as it can build up in pool water which may require pool water to be dumped or backwashed to reduce the stabiliser concentration.
What levels of chemicals do I need?
A sufficient level of active disinfecting chemicals must be continually present in the water to destroy all harmful microorganisms.
Free chlorine can be measured on a test kit using DPD No. 1 tablet.
Combined chlorine can be measured by a test kit using a DPD No. 3 tablet.
Ask your pool technician how to sample for free and combined chlorine. There should always be less combined chlorine than free chlorine in a well-managed pool.
Unstabilised (indoor) pools and spas – chlorine
It is important to maintain a free chlorine level of at least:
- 1 milligram per litre for water temperatures below 26 °C
- 2 milligrams per litre for water temperatures above 26 °C.
Stabilisers should not be used in a spa or indoor pool.
Stabilised (outdoor) pools – chlorine
It is important to maintain, at all times, a free chlorine level of at least:
- 2 milligrams per litre for water temperatures below 26 °C
- 3 milligrams per litre for water temperatures above 26 °C.
Stabiliser (isocyanuric acid)
Isocyanuric acid should be maintained at a level between 30 and 50 milligrams per litre.
Stabiliser is recommended in outdoor pools that use chlorine.
Acidity or pH level
The pH reading is a measure of how acidic (low pH, below 7) or alkaline (high pH, over 7) the water is, with a pH reading of 7.0 being neutral.
The effectiveness of the disinfecting chemicals depends on the pH of the water. Chlorine works best when the pH reading is between 7.2 and 7.8, with a reading of 7.5 ideal for bathers.
Factors that can affect your pool's pH level include:
- heavy rain
- the number of swimmers in the pool
- use of chemicals.
Remember to regularly check the pH level daily.
Regular water testing is important
Check the chemical levels in your pool or spa water at least once a day.
The most important chemical levels are the:
- free chlorine or free bromine levels
- pH levels
Free chlorine and free bromine levels are generally measured using DPD 1 reagents.
pH levels are measured using Phenol Red reagents. Both DPD1 and Phenol Red are available in a tablet form from pool equipment stockists or shops.
If you use stabiliser (isocyanuric acid) in your pool or spa you should also check the level of this chemical at least once a day.
On hot days, test the water in swimming pools before your first swim and at least once again during the day.
Heated spa pools should be tested at least twice a day whenever in use.
If the results show chemical levels are too high or too low, you will need to take corrective action.
Never add chemicals while people are in the water. Allow at least 30 minutes for chemicals to dissolve into the water before anyone enters the water.
For advice on the types of test kits available contact your trained local pool and spa technician.
Manual or automatic dosing?
Chemicals can be added to water manually or via an automatic dosing system.
Automatic systems are simpler for maintaining water quality because they test the water chemistry and add the required amount of chemicals.
For busy people the use of an automatic chlorine dosing system or salt pool generated by electrolysis is a good idea. For home owners with more time, a hand dosed system can be used. Automatic systems can be programmed to operate when you are absent from the home.
Water balance is a measure of the concentration of calcium salts in relation to other chemicals in the water.
It involves measuring:
- the calcium hardness
- total alkalinity
- pH (acidity) of the water.
Keeping the water in your pool or spa balanced will help you to get the most from it.
Balancing your water will prevent premature erosion or scaling of pool and spa surfaces, pipes, filters and other equipment.
Your trained local pool and spa technician can help you to balance your water.
Can I use bore water to fill my pool or spa?
It is preferable to fill your pool or spa with scheme drinking water because it is treated and safe, good quality water.
If you use bore water you will need to increase the quantity of chemicals you use (especially if the water contains a lot of iron) and this will add to your costs.
Algae in swimming pools
Algae are single-celled organisms that grow quickly in sunny and warm conditions and can turn the water in your swimming pool green within a few hours. Chlorine will help prevent growth of algae.
You can use a brush to remove algae from pool surfaces. The next day, vacuum the settled algae from the floor of your pool – do not try to remove it by running the filter.
Be sure to check the total alkalinity, pH and calcium hardness before you allow anyone to swim.
Have your trained pool technician check the level of phosphorus in your scheme water supply to make sure that the pool water is not affected. Chemicals can be added to fix this.
Faeces in swimming pools
Young children can occasionally have a faecal accident while swimming.
If this occurs, it is best to get everyone to vacate the pool and remove as much of the solid faeces as possible using a fine mesh scoop. If the child (or adult) has had diarrhoea, contact your trained technician to arrange to super chlorinate the pool.
As much as possible, do not permit any person who has contracted cryptosporidiosis or giardiasis in the last fortnight to swim in your pool or spa, as they are likely to still be infectious and can spread harmful micro-organisms into your pool.
If the pool is small, draining and scrubbing it is an option. Use a household bleach to sanitise the plastic pool and leave to dry in the sun.
Be sure to check the chlorine levels have returned to regular levels before anyone re-enters the swimming pool.
Strong chlorine smell in swimming pools
A strong chlorine-like smell can irritate the eyes, nose and skin.
Contrary to popular belief, the smell is caused by too little chlorine rather than too much. If your pool smells strongly, check the chlorine level each day before you enter the pool or spa.
Pool covers and winter maintenance
Pool covers are an excellent method of saving water.
Pools with solar heaters will raise the surface temperature and encourage evaporation. In an average 8 metre by 4 metre swimming pool without a cover, daily evaporation of 15 millimetres can be expected, leaving the pool owner to think that the pool has sprung a leak.
A pool in summer with a pool cover may artificially raise the temperature of water near the surface encouraging an algal bloom. Advice from your trained pool technician may be very valuable to manage these conditions.
If a pool or spa is not in use over winter, fit a secure pool blanket and arrange the pool or pool motors to operate one hour week injecting a small quantity of chlorine to prevent bacterial growth.
Prior to the next season of use, the pool or spa should be vacuumed.
- Follow good pool water hygiene practices to keep your family and friends safe in the water.
- Check the chemical levels in your pool at least once a day, more often in hot weather.
- The most important chemical levels to check are the free chlorine and the pH levels.
- Allow at least 30 minutes for chemicals to dissolve into the water before anyone enters the water.
- Never add chemicals while people are in the water.
- Always follow the instructions on pool chlorine containers in relation to safe handling and disposal of the product.
Where to get help
Advice on water treatment is available from:
- your local pool and spa technician
- pool chemical suppliers
- Water Unit, Environmental Health Directorate Department of Health WA
This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.