Water testing: the basics

Macquatics Training
By John McKenny*, Macquatics Training
Monday, 07 November, 2016

Water testing: the basics

This is the third in a series of non-technical articles written to assist pool techs understand water testing. Keep your costs down and your pool clean and safe for swimming by following ‘Good water matters’ in each publication.

Obtaining reliable results, then knowing what to do if chemicals need to be added, is the key to having clean and safe water for swimming.

Why test?

I am sometimes asked this question. The answer is that any pool which is using chemicals (and there are some which don’t — natural pools are ‘chemical free’) must be tested regularly to ensure the water is clean and safe to swim in. There must be enough sanitiser (chlorine or bromine) to ensure continuous and effective sanitation, but not too much — this can cause swimmer discomfort and/or high pH. Often ignored, pH must be between 7.3 and 7.6 and ideally at 7.4. Only testing will show the actual levels.

How often?

In New South Wales, all public pools — council, motel, rooftop, resort, water play parks and the like — must be tested daily for sanitiser and pH when open or available to the public. Other tests, such as calcium and cyanurate/cyanuric acid/stabiliser in outdoor pools, must be tested weekly.

The test kit

For less than $50, you can buy an easy-to-use water test kit to obtain the chlorine and pH levels of the pool water. By following the simple directions supplied, these important tests can be done in three to four minutes. The kits usually allow you to test for alkalinity too, but in my opinion, this test is much less important.

These test kits have shown to provide reasonably accurate results. There are also much more accurate photometers available, which are normally used at large swim centres and are far more expensive. Remember: if you follow the directions, you’ll realise how easy it is.


Use a clean, plastic container (a large plastic mug is ideal). After rinsing, take the sample at the deep end and at least 30 cm below the surface.


Don’t delay — test the water immediately before the chlorine weakens. A delay of five minutes is too long, so if this happens, return to the deep end of the pool and take a fresh sample.

Using a two-chamber basic pool water test system
  1. Rinse the testing chambers twice with pool water, fill them to the 10 mL mark shown on the testing chambers with the sample to be tested, then follow the test instructions supplied with the kit.
  2. Add the correct number of ‘DPD No.1’ or chlorine drops to the chlorine side and the drops of phenol red indicator to the pH side. Place the caps provided for the testing chambers on the sample tubes, then gently invert the chamber to mix the sample and the added test reagent. Observe the colour in each chamber and decide which colour on the test chambers matches the sample colour. This will be your chlorine and pH results of the sample.
  3. If you’re using tablets to test the water, you should never touch them. Instead, carefully pop the tablet from the blister pack directly into the water sample. Sometimes these tablets will take a while to dissolve and sometimes a crusher rod is used to crush the tablet inside the test chamber holding the water sample to be tested. If this is the case, always rinse the crusher rod in clean water before and after using it. Also, never hold the test chamber when using the crushing rod to break down the tablets. If the test chamber breaks, you could end up with a hand injury, so always place the test chamber on a smooth, flat and firm surface before applying force with the crushing rod. Discard tablets if dropped, touched or contaminated in any way.
  4. Keep records. As you obtain a result, write down the date and test result.
  5. Rinse the test chambers after testing and leave to drain. Leaving the test chambers with the test reagent in them can cause a discolouration of the surface, which can cause future tests to read inaccurately.

Strange results

Initially, you can expect to obtain strange results now and then. It’s best to write all results down, but take another sample and run the tests again. The same result could mean that you have a problem, so contact either myself or your pool shop for advice. I’m happy to assist.

Anything else?

Actually, yes! It’s an excellent idea each month to do a pH test on your incoming water to the pool, then you’ll know what to expect each time you backwash the filter or do a pool top-up. If you have cartridge filters, they are normally hosed off, so it won’t be important until you need extra water in the pool.

Domestic water supplied on the Australian east coast is quite often low in calcium with reasonable alkalinity and pH, along with an insignificant amount of chlorine. Out west, the situation is much different, with test results being dependent upon whether the water comes from dams, creeks, rivers, tanks or artesian bores. Quite often, this water is difficult to adjust and hard to maintain for pleasant swimming.

Now that you have the water testing sorted, the next step is to know what to do about the results: adding which chemical, how much, where, when and why. This will be the next topic in this series.

Have a question or need further assistance? Free and no-obligation assistance is available by contacting me through my website (www.macquaticstraining.com) or email (jsmck@bigpond.net.au).

*John McKenny has managed and leased swim centres for more than 30 years. He commenced TAFE teaching in swim centre operations and management 25 years ago and continues today. John is the author of The Complete Swimming Pool Handbook and The Leisure Pool and Spa Handbook.

Image credit: ©stock.adobe.com/au/sirirak

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