Over the last few years there has been a heightened awareness of the threat imposed by Cryptosporidium (and Giardia) – protozoal organisms whose cysts are resistant to chlorine and which can cause gastro-intestinal illness. Swimming Pool Water and a subsequent technical guidance note advise on minimising the threat and how to employ good filtration practices to deal with diarrhoeal contamination of pools.

However, there were doubts about exactly how effective different filtration regimes are against the cysts. So PWTAG has sponsored research at Swansea University’s Centre for Water & Environmental Management, using fluorescent crytosporidium cyst-sized polystyrene granules.

The first runs confirmed that coagulation can increase the rate of removal from as low as 50% to 95% or more. But the research also suggested that higher than traditional levels of coagulation dosing gave the best results. This raised the issue of whether these higher rates should be used routinely, or only when diarrhoea had been introduced to the pool and the pool is out of use for the six turnovers needed to be sure all the water has been through the filters.
So, further research examined the effect on pools of dosing PAC at ten times the normal rate. The pressure differential across the filtes rose four times as rapidly. This means that applying the higher dosing rate routinely might well necessitate either upgrading pumps or increasing backwashing frequency. So it should probably be reserved for incidents of diarrhoea in the pool, or when it is discovered that the plant has been operating imperfectly.

Work at Swansea is continuing. PWTAG is funding a short-term project examining the effect of higher than recommended filtration rates on cyst removal. A three-year project, starting in October 2006, will look at the effects on filtration effectiveness of temperature, flow rates, different coagulation regimes, sand depth and alternative media. Live Cryptosporidium cysts will be used in some of this work. PWTAG is making a significant financial contribution to this important work.

A special session of the March 2005 PWTAG meeting was devoted to presentations on this subject

Since 2003 there has been regular if infrequent media coverage linking swimming pools and asthma The origin for this has been a series of published reports by Professor Alfred Bernard in Louvain, Belgium. He suggests that nitrogen trichloride (an irritant disinfection byproduct in the air above less than perfectly managed pools, particularly where venitlation is poor) damages the lungs of children, making them prone to asthma.

Although doubts have been raised about the research methods, the work is taken seriously by authorities in the UK; and it continues. The levels of nitrogen trichloride quoted in some of these studies are higher than would be expected in a well-run UK pool.The rather generous upper limit suggested by some European authorities of 0.5 milligrams per cubic metre was exceeded. So PWTAG sponsored a pilot investigation by Oakland Calvert Consultants of six UK pools, using a nitrogen trichloride detector.

Results showed levels of nitrogen trichloride ranging from 0.17 to 0.36 milligrams per cubic metre. The variation correlated with subjective assessments of irritation. The results did suggest that under higher bather load the 0.5 limit might well be breached.

This work was published in Recreation magazine (and is on www.pwtag.org). It emphasises the need for good water management and ventilation, and for bathers to follow their noses.

PWTAG is actively engaged in discussions with academics, health authorities and other on this and related issues. It has also supported important funding applications in this area.

After careful review, it has been possible to draw some tentative conclusions from a difficult two-year laboratory study conducted during 2004. The effect of different degrees of calcium hardness on prepared grout prisms was measured. In contradiction to what had been claimed by advocates of calcium rather than hypochlorite disinfection, hardness did not seem to affect grout loss. PWTAG’s conclusion is that properly prepared and cured grout should not present the erosion problems that have certainly been encountered in the past.