Lovibond® Water Testing Tintometer® Group

June 2017 - The Clarity of Pools

The Importance of Measuring Turbidity

“Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.”

No one would disagree that cloudy pool water is undesired. It can have a serious detrimental effect on swimmer safety. It also makes lane markings and items on the pool bottom difficult to see. Impairing the visibility of the pool floor is particularly dangerous if a bather gets into difficulties. Tragically, on average, around 400 people drown around the UK every year*. Obviously, these numbers include accidents in rivers, lakes and the sea, but there is a significant risk of potential drowning in pools especially for children not yet competent in swimming skills. A struggling swimmer can quickly go under water. It is essential that the lifeguard on duty is able to take appropriate, immediate action. Every second counts for successful rescue, intervention and resuscitation.

Cloudy or hazy water is caused by suspended particles that are usually invisible to the naked eye. These impurities are introduced from a variety of sources including, but not limited to, air debris, dirt, pollen, algae, cosmetics and microbial organisms. Unsurprisingly, some of the main contributors to these impurities are bathers and source water.

Cloudiness is caused by a rise in turbidity of the pool water. To ensure that the pool is safe, this turbidity must be measured on a regular basis. This is particularly true in the case of public pools although even domestic pool owners should be aware of the potential consequences.

In the United Kingdom, there are no formal standards for water quality in the swimming pool industry. However, the widely acknowledged PWTAG guidelines suggest the turbidity of pool water should be no greater than 0.5 NTU (Nephlometric Turbidity Units). How many of us, however, really take this seriously? PWTAG also recommends that Turbidity should be measured using a nephelometer, more commonly referred to as a turbidimeter.

A turbidimeter is an electronic device which uses the principle that light passing through a substance is reflected or scattered by particulate matter suspended in the substance. Unlike electronic photometers which are commonly used to measure disinfection and pH levels, Turbidity meters simply measure the optical properties of the pool water and do not require any additional reagents.

As the image shows, it is difficult for the human eye to distinguish NTU levels below 20, so an electronic device is essential to accurately measure to the PWTAG recommendation. Yet how many pool operators still use the guideline ‘if you can see the bottom of the pool, everything is OK’? And is this really sufficient?

Monitoring the turbidity of the pool water is not only essential for bather safety but can also indicate other problems within the pool water chemistry such as inadequate Chlorine or, incorrect pH levels. It can also indicate a change in filtration performance.

So why does the turbidity of a pool increase?

Poor pool water chemistry – if the chlorine or pH levels are incorrect, the quality of the water will decrease rapidly and cause the turbidity to increase. Furthermore, poor water balance or an increase in levels of TDS (Total Dissolved Solids) and phosphate can affect the cloudiness of the pool. By strictly following best practice for Balanced Water (Langelier Index) and reacting quickly and accordingly, the risk of too turbid water can be greatly reduced, though levels should still be measured. Increased levels in turbidity can also provide an indication of background levels of cryptosporidium though further specific microbiological analysis should be carried out.

Filtration problems – today, there are numerous types of various filtration media available including traditional sand, glass and plastic based products all of which claim to reduce the water turbidity. Regulated pump running times and regular filter maintenance will increase effectiveness. However, how do we know they work if the turbidity levels are not being monitored? An increase in turbidity can indicate filter problems including dirty filters, a poor back washing regime or problems with flow rates and sizing.

Regular monitoring of turbidity is, therefore, essential: for bather safety; assurance that you are meeting the current guidelines; as an aid to identify problems with water quality before they become too severe; to ensure the filtration set is correct and running efficiently.

* The UK national drowning prevention strategy 2016 - 2026

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