A hot tub is a recirculating body of warm water, and the perception of shared water as unsanitary is not unfounded. Whether a hot tub is “gross” depends entirely on maintenance, not the vessel itself. The warm temperatures that make soaking enjoyable also create an ideal environment for microorganisms to thrive if not properly managed. When water chemistry is neglected, the spa quickly becomes a breeding ground for bacteria and other contaminants.
How Contaminants Enter Hot Tub Water
The primary challenge to maintaining clean hot tub water is the volume of organic material introduced by users, known as the organic load. Every person who enters the spa brings millions of skin cells, sweat, hair, cosmetics, lotions, and detergents left on swimwear. These inputs are compounded by environmental factors like dirt, leaves, and airborne particles.
The high temperature of the water, typically between 100°F and 104°F, accelerates the consumption of chemical sanitizers like chlorine and bromine. As sanitizers are depleted by the organic load, bacteria begin to attach to the hot tub’s plumbing and shell. This attachment leads to the formation of biofilm, a slimy protective layer that shields microbes from the remaining disinfectant.
Biofilm can harbor bacteria like Legionella and Pseudomonas aeruginosa, creating a continuous source of contamination, even if the water is regularly treated. This protective layer dramatically increases the demand for sanitizer, making it difficult to keep the water balanced and clean. Furthermore, substances like lotions and oils react with sanitizers, forming chemical byproducts that interfere with effectiveness and contribute to poor water quality.
Common Health Risks Associated with Poor Maintenance
Exposure to inadequately sanitized water can lead to infectious outcomes, primarily affecting the skin and respiratory system. One common skin infection is folliculitis, often called “Hot Tub Rash,” caused by the bacterium Pseudomonas aeruginosa. Symptoms appear as an itchy, red, bumpy rash, often with pus-filled blisters around hair follicles.
This rash is worse in areas where a swimsuit holds contaminated water against the skin for an extended period. While mild cases often clear up within a week or two without medical intervention, the bacteria’s presence indicates a failure in the disinfection system. A more serious respiratory risk comes from Legionella pneumophila, the bacteria responsible for Legionnaires’ disease (a form of pneumonia) and the milder Pontiac Fever.
These bacteria thrive in the warm, stagnant conditions of poorly maintained hot tubs. They are transmitted when users inhale aerosolized water droplets generated by the jets and bubbles. Unbalanced water chemistry can also cause non-infectious risks, such as eye irritation and dry, itchy skin from improper pH or excessive chlorine byproducts.
Guidelines for Ensuring Water Safety
Preventing illness requires consistent maintenance and thoughtful user behavior. Owners must prioritize maintaining proper water chemistry by regularly testing the water’s pH and sanitizer levels. The ideal pH level should be between 7.2 and 7.8, ensuring bather comfort and maximizing disinfectant effectiveness.
For sanitation, the Centers for Disease Control and Prevention recommends maintaining a free chlorine level of at least 3 ppm or a bromine level of 4 to 8 ppm. Water should be tested with reliable test strips or a digital kit at least twice a week, and before each use if the tub is used frequently. A weekly shock treatment is necessary to break down organic compounds and reactivate the sanitizer.
All users should practice mandatory pre-soak showering with soap to remove body oils, cosmetics, and sweat, which significantly reduces the organic load. For owners, proper filtration requires regular cleaning of the filter cartridge and ensuring the recirculation system runs for several hours daily. Finally, the entire volume of water should be drained and replaced every three to four months for private tubs, with the plumbing flushed using a biofilm remover before refilling.