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Ask The Expert



If you have a question or query on a wet leisure project or product, contact SPATA / BISHTA via SPN, the UK industry’s longest established magazine. Email:

“I keep hearing mention of the OECD test protocol for water treatment, what is this?”

The Organisation for Economic Co-operation and Development (OECD) is an intergovernmental organisation in which representatives of 34 industrialised countries from around the world meet to harmonise policies and respond to international problems. The OECD have provided a guidance document demonstrating the efficacy of Pool and Spa Disinfectants in Laboratory and Field Testing. The document is 30 pages long, but the main information is contained in pages 19 – 29. An electronic copy of the document can be obtained from and please note that PWTAG have a copy on their website at: The issue addressed in this OECD guidance is covered in item 7 on page 20 and provides details of how: “… the proposed new disinfectant is effective against suitable indicator species of pathogens in the major classes (bacteria, protozoa and viruses) of human pathogenic microorganisms found in swimming pool and spa pool water”. Any disinfectant in use in accordance with manufacturer’s instructions must be safe to human health and the environment and a risk assessment is needed as part of the process. It must be equivalent in its efficacy to the performance of hypochlorous acid / hypochlorite. The guidance document provides information on Laboratory Testing in items 10 – 14 on pages 21 – 26 and on Field Testing in items 21 – 22 on pages 26 – 29.

Companies are encouraged to demonstrate their products can meet the OECD test protocol and any products they intend to use, or recommend should be able to pass this test.

For clarification, the disinfectants currently recognised for water hygiene management by PWTAG are chlorine, bromine and PHMB.


Howard is an independent consultant, a Technical Adviser to BISHTA and SPATA Chairman of the BISHTA Technical Committee and a Member of SPATA’s Technical Committee.


Peter is an independent consultant and SPATA’s Technical Adviser. He is a SPATA Inspector and Chairman of SPATA’s Technical Committee.

“Why do I need an air gap in the water supply to the pool?”

In the UK, the water suppliers have, by law, to supply drinking water which is chemically, medically and biologically safe for human consumption, that is to say potable water. When bathers swim in the pool, they can contaminate the pool water with perspiration and other bodily pollutants. Additionally, in outdoor pools and indoor pools, with patio doors open, wind blown pollutants, such as algae, can get into the water. In a well maintained pool, these pollutants are eliminated by the water treatment chemicals, by oxidising disinfectants. However the water suppliers have to judge pool water on the worst case scenario of a badly run pool with poor maintenance and consequently high counts of pollution. Consequently, they classify pool water as Category Five which poses the greatest risk to health. Water is supplied under pressure so that it flows out of the tap easily and quickly. If there is a failure in that pressurised mains water system, then it is possible that a vacuum can occur and the supply water travels in reverse. A hose left dangling in the pool water, while topping up the pool, connected via an open tap can in theory, stop filling the pool and start sucking water out of it. This means that pool water will enter the mains water supply. It is this potential issue that the water suppliers are concerned about and although it may seem unlikely to happen, the water companies have recorded incidents where this has occurred. Under the requirements of the Water (Supply and Fittings) Regulations 1999 the connection of a water supply directly to a swimming pool has to be via an air gap. The simplest example is the hose pipe connected to a tap. The end of the hose should not be put into the water but be suspended over it by at least 150mm and fixed so that the hose cannot easily drop into the pool water. Where automatic top up is fitted to the pool, the main supply should be directed to a holding tank, rather like a toilet cistern. The flow into it being controlled by a float valve and the supply to the topping up device on the side of the pool falling under gravity. Alternatively a float switch and solenoid valve can be used with an air gap under the solenoid above a pipe to the pool. Without the air gap, either from a supply tank, or under the hose on the side of the pool, the law of the land is being broken. Finally, as an additional point, it is also useful for all outside taps to be fitted with a double check valve and to be protected from freezing.

34 October 2013 SPN

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