Testing swimming pool and hot tub water: Key terms and questions answered

Some helpful terms:

Alkalinity: A measure of the water’s ability to resist changes in pH.
Bromine: A halogen disinfectant, often used in hot tubs and spas due to its effectiveness at higher temperatures.
Calcium Hardness: The amount of dissolved calcium in the water.
Chlorine: The most commonly used pool disinfectant; exists as free chlorine (available for disinfection) and combined chlorine (chlorine bound to contaminants).
Colony Count: A measure of the number of bacteria colonies present in a water sample.
Colorimetric Methods: Water testing methods that involve adding reagents to a water sample to produce a colour change proportional to the concentration of the substance being tested.
Cyanuric Acid: Also known as a chlorine stabiliser, it helps protect chlorine from degradation by UV light.
Disinfectant: A chemical substance used to kill harmful bacteria and other microorganisms in pool water.
Dissolved Solids: The total amount of dissolved minerals and other substances in the water.
Electrochemical Methods: Water testing methods that use electrical measurements to determine the concentration of a substance.
E. coli: A type of bacteria that indicates faecal contamination of water.
Free Chlorine: The amount of chlorine available to kill bacteria and other contaminants.
Hydrogen Peroxide: A powerful oxidising agent sometimes used in conjunction with other disinfectants.
Normal Operating Procedure (NOP): A documented set of instructions for operating and maintaining a swimming pool.
NTU (Nephelometric Turbidity Units): A unit of measurement for turbidity, or the cloudiness of water.
Ozone: A powerful disinfectant that is very effective at killing bacteria and other microorganisms.
pH: A measure of the acidity or alkalinity of the water.
PHMB: A disinfectant alternative to chlorine and bromine.
Phosphate: A nutrient that can promote algae growth in pool water.
Photometer: A device that measures the intensity of light passing through a water sample to determine the concentration of a substance.
Salinity: The amount of dissolved salt in the water.
Test Strips: A simple and economical way to test water parameters, producing indicative results.
Total Alkalinity: A measure of the total amount of alkaline substances dissolved in the water.
Total Chlorine: The sum of free chlorine and combined chlorine.
Turbidity: A measure of the cloudiness or haziness of water, indicating the presence of suspended particles.
Water Balance Index: A calculation used to assess the water’s tendency to be corrosive or scale-forming.

Short-Answer Quiz

Why is regular water testing crucial for swimming pools?
Explain the difference between free chlorine and combined chlorine.
What are the benefits of using bromine as a disinfectant, particularly in hot tubs and spas?
Why is cyanuric acid often added to outdoor pools?
What problems can arise if calcium hardness levels are too low or too high?
What is the role of total alkalinity in maintaining pool water quality?
How does salt water chlorination work as a disinfection method?
What does turbidity indicate about the water quality, and what are some potential causes of high turbidity?
Describe the Palintest Water Balance Index and its significance.
What are some best practices for ensuring accurate results when using photometers for water testing?

Short-Answer Quiz: Answer Key

Regular water testing is crucial to ensure bather safety and comfort, effectively remove contamination, maintain the pool and its surroundings, and control chemical usage. Failure to test correctly can lead to bather illnesses, irritation, and pool maintenance issues.
Free chlorine is the chlorine actively available to kill bacteria and other contaminants. Combined chlorine is chlorine that has reacted with nitrogen-containing compounds in the water, forming chloramines. While combined chlorine still has some disinfecting power, it is less effective than free chlorine.
Bromine is more active at higher pH levels and temperatures, making it a suitable disinfectant for hot tubs and spas. It is also more stable than chlorine and can be gentler on sensitive skin.
Cyanuric acid, also called a stabiliser, helps protect chlorine from degradation by ultraviolet (UV) light from the sun, making it particularly beneficial for outdoor pools.
Low calcium hardness can cause the pool water to erode grout and pool surfaces, while high calcium hardness can lead to scale formation and “hard water” marks.
Total alkalinity acts as a buffer, preventing drastic pH fluctuations when the pool is in use. Maintaining appropriate alkalinity levels ensures the effectiveness of the disinfectant and contributes to bather comfort.
Salt water chlorination utilises electrolysis to convert dissolved salt (sodium chloride) into hypochlorous acid and sodium hypochlorite, which act as the sanitising agents in the pool.
Turbidity, the cloudiness of water, indicates the presence of suspended particles. High turbidity can be caused by poor water chemistry, deteriorating filter quality, inadequate backwashing, or incorrect flow rates/pipe sizing. It can also impact the effectiveness of disinfection.
The Palintest Water Balance Index is a calculation based on calcium hardness, total alkalinity, and pH. It indicates whether the water is balanced, corrosive, or scale-forming, guiding adjustments to protect pool equipment and surfaces.
Best practices include regular calibration checks, adherence to test procedures, clean test tubes, careful reagent handling, proper blank usage, thorough tablet crushing, avoiding shaking or inverting the test tube, using the light cap, and stirring with a crushing rod.