Two sources of contamination of a hydrotherapy pool by environmental organisms

As a result of occasional water discolouration, the hydrotherapy pool of a large teaching hospital was monitored for free and combined chlorine, alkalinity, calcium hardness, total dissolved solids and cyanuric acid levels together with bacteriological analysis. The hose pipe supplying the pool and the dual water pumps were also examined as potential sources of bacterial contamination. The pool water yielded high counts of Pseudomonas vesicularis, Pseudomonas aeruginosa, and CDC Group IV C2, even in the presence of adequate levels of free chlorine. This was found to be due to high concentrations of cyanuric acid which resulted in a 'chlorine lock'. The source of the P. vesicularis and CDC Group IV C2 was found to be the pool hose and this problem was alleviated by flushing it with water each day before use. The source of the P. aeruginosa was the pool pumps, and was eradicated by regularly shock dosing them with 6-8 ppm of free chlorine.