SPN (Swimming Pool News) October 2021

Page 36


Why Do We Need To Test Our Water? In this article Colin Day from Lovibond® Tintometer – who have recently partnered with STA – answers some common questions on water testing


veryone would agree that water is a vital component in any pool and having good water quality is essential. To achieve the desired quality requires both testing and knowledge surrounding water chemistry and the testing processes involved.

WHY DO WE NEED TO TEST OUR WATER? As we all know, water has to be treated to keep it safe. How can we treat the water and know what to add if we do not know the levels? Therefore, water must be tested regularly to ensure: • There is sufficient treatment • The water is safe and comfortable for bathers • Plant and equipment is well maintained • Compliance to guidelines and operation procedures.

WHAT SHOULD WE BE USING TO CARRY OUT THE TESTING? A professional test kit must be used. This can be either a coloured glass-based comparator system or photometer. To ensure readings are correct, the equipment must be spotlessly clean and the correct reagents used. Operators must also follow the instructions and keep photometers calibrated.

WHICH IS BEST FOR ME – A COMPARATOR OR PHOTOMETER? Both systems are acceptable and the final selection is down to end user preference. Photometers will give more precise readings (i.e., down to 0.1mg/l for chlorine) but can drift out of calibration. Glass comparators have fixed colours so cannot go wrong, but they are not suitable for all users (please note that the colours on plastic-based discs will fade over time).

HOW OFTEN DOES A PHOTOMETER NEED CALIBRATING? All photometers should be checked regularly against known standards. With most professional systems, reference kits are available which enable users to check units easily and quickly on site. For continued accurate operation, it is recommended that photometers are factory checked every year.

WHAT PARAMETERS SHOULD WE BE TESTING AND HOW REGULARLY? There are numerous parameters that can be measured in pool water but the five most important are (assuming chlorine-based disinfection): • Chlorine (free and total) – Test frequently throughout the day in accordance with risk assessment and operating procedures (work out combined chlorine) • pH – Must always be tested the same time as chlorine - doing one without the other is pointless • Total Alkalinity – Measure weekly • Calcium Hardness – Measure weekly • TDS – Measure weekly or more often if issues.

WHY SHOULD FREE CHLORINE AND PH ALWAYS BE MEASURED TOGETHER? Not only is pH important for bather comfort and to ensure that the water is not scale forming or corrosive, but it also affects the efficiency of the chlorine. As pH rises, the amount of free chlorine that is available as hypochlorous acid decreases. If levels increase above 7.8 the chlorine efficiency declines so much that pools should consider closing even if free chlorine readings are within range. Therefore, they should always be tested together.

WHAT IS TDS? TDS stands for Total Dissolved Solids. It is the sum of the weight of the soluble compounds in the water. Normal potable drinking water contains around 600mg/l, brackish water 3000mg/l and seawater typically 35000mg/l. In a pool TDS can rise with the addition of chemicals and contamination introduced by bathers. High levels of TDS will impair the performance of the disinfectant and other treatment. As it is ‘dissolved’, TDS cannot be removed by filtration, so can only be controlled by dilution. Ideal TDS is no more than 1000mg/l above the incoming level.

WHAT IS TURBIDITY AND IS IT IMPORTANT IN SWIMMING POOL WATER? Quite simply it is a measurement of the cloudiness of water. High turbidity means the

Not only is pH important for bather comfort and to ensure that the water is not scale forming or corrosive, but it also affects the efficiency of the chlorine” 34 October 2021 SPN 34_SPN_October_21_STA.indd 34

water is cloudy and low turbidity means it will be clear. Turbidity is normally measured in NTU (Nephelometric Turbidity Units). In the UK the maximum value allowed at a consumer drinking water outlet is 4NTU and is normally around 0.5NTU. Is it important in pool water? PWTAG say yes and that levels should be no more than 0.5NTU, so the same level as drinking water. Poor turbidity can: • Make the water dangerous, especially if you cannot see the bottom of the pool • Indicate poor water chemistry • Indicate poor circulation or filtration • Prevent underwater cameras functioning correctly. Finally, testing should always be carried out correctly, as you are only measuring very small quantities. Here are some tips on good practice when it comes to water testing to help ensure your results are accurate and correct: • Follow manufacturer’s instructions • Use the correct tablets • Allow reaction time if specified • Keep equipment clean and dry • Wash and dry hands prior to testing • Never handle the tablets • Check and calibrate photometers regularly • Ensure those testing are trained and understand its importance • Carry out testing as quickly as possible after taking the sample • Check sample tubes and discard any dirty or scratched vials. STA offer a regulated four-hour Swimming Pool Water Testing qualification, which is perfect for those responsible for carrying out routine pool water tests. Many lifeguards or pool hirers for example must test pool water as part of their job role, and this qualification gives them the basic information and skills necessary to test swimming pool and spa water competently, whilst providing a basic understanding of the outcomes of those tests. STA 01922 645097 www.sta.co.uk STA is pleased to announce a new partnership which will see Lovibond® Tintometer pool water testing equipment and reagents added to the STA Swim-Shop with a 10% discount off list price for STA members. Visit the STA’s online store at https://store.sta.co.uk/ for details.

www.swimmingpoolnews.co.uk 19/10/2021 23:44