During retirement I discovered the physical and emotional benefits of swimming laps in my local high school swimming pool several mornings a week. The water is clear, refreshing and free of contaminants and micro-organisms as expected. As an owner of an indoor hot tub, I realized regular weekly attention to testing and maintaining water quality was necessary but was a chore I frequently neglected.
I was curious to learn how large public swimming pools such as the YMCA, Boys and Girls Club, colleges and high schools maintain safe, inviting water day after day. Achieving safe refreshing pool water is called proper water balance. Water balance in a swimming pool requires regulation of temperature, pH, alkalinity and sterilizing capacity. Large public pools monitor and adjust water balance automatically; here is how it is done as explained to me by Roger Connelly, supervisor of Building and Grounds, at Southwestern Central School during a tour of the pool maintenance facilities in early March 2014.
Elimination of bacteria and viruses is accomplished with a sterilizing chemical, chlorine. Chlorine sensors in the pump circulation automatically keep the concentration at 1.0-1.5 ppm (parts per million).
Refreshing, clear, safe swimming pool water is maintained by the Southwestern Central School water balance system. This image demonstrates the heater on the left and sand filters to the right. The water pump and chlorine reservoir are near the floor behind the sand filters.
Photo by Robert M. Ungerer
Of utmost importance is the acidity and alkalinity of the water. This is measured as the potential hydrogen hence pH measured on a scale from 1 to 14. Seven is neutral so less than 7 is acid and over 7 is alkaline or basic. The desired swimming pool pH is 7.5. The human body has a pH of 7.3-7.5. Vinegar has a pH of 3, therefore is acidic. Swimming in vinegar might taste fine but would irritate the eyes and skin as well as erode pool pipes, tiles and cement. On the other hand baking soda has a pH of 8.3. Swimming in a solution of baking soda also irritates eyes and creates chemical deposits and scales on pool walls and clogs filters and pipes. If the pH of pools is too high, meaning alkaline or basic, muriatic acid is added automatically to lower the pH. If the pH is too low, meaning acidic, a buffer, bicarbonate is added manually to raise the pH without compromising chlorine's killing effect. Water temperature is maintained between 78-82 degrees F (Fahrenheit). Competitive swimmers require the pool to be at the cooler temperature to prevent overheating during a race. Young children learning to swim tolerate more time in the water if warmer.
An extensive ventilation system in the ceiling achieves an air temperature 2 degrees above the water temperature, removes chlorine vapor and lowers humidity by mixing outside air with pool room air. To prevent pool room humidity and chlorine vapors from entering school hallways when doors are opened, negative pressure is maintained in the pool room.
A visit to the pump room demonstrated in the accompanying photograph reveals the water pump which runs 365 days a year, pool heater, long cylindrical sand filled filters and chlorine reservoir. The entire pool volume turns over four times every 24 hours. The sand filters which remove body oils, lotions and normal exfoliated skin are cleaned automatically by reversing water flow to flush contaminants into the storm drains.
Pool heater output-1.5 million BTU (British Thermal Units).
A typical residential furnace generates 100,000 BTU.
Volume- 195,000 gallons. A backyard pool may hold 30,000 gallons.
Water is tested three times daily for chlorine and once a day for pH and alkalinity.
Pool operation is conducted by four SWCS employees who are Certified Pool Operators by completing a three day course. Recertification is required every three years. The New York State Health Department conducts unannounced inspections of the pool at least once a year to monitor safety equipment, cleanliness and compliance with state administration.
Local public swimming pools require huge costs to construct and maintain. We are fortunate to have pools because they enable children and adults to learn a lifetime skill, swimming, for survival in water, fun and exercise. Jump in, science and technology allow you to swim year round.