Swimming-pool water is only as safe as the chemicals used to maintain the pool. Chlorine is the chemical most public and private pools rely on for disinfection, and it usually is effective and safe. The Centers for Disease Control and Prevention website states that chlorine levels of 1.0 to 3.0 ppm, or parts per million, fall within most health department guidelines. Chlorine interacts with the water and contaminants in it to alter pool pH and create secondary compounds that cause troubles of their own. A pool's pH is a measure of the acidity or alkalinity of the water.
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Skin and Eyes
Excess chlorine levels in the pool result from human error or equipment malfunction. When chlorine levels spike, the water becomes toxic to humans. Acute over-chlorination in pools causes swimmers to experience moderate to severe eye irritation. They experience burning in their nasal passages and mouth if they inhale the over-chlorinated water. Swimmers also develop rashes and irritated skin when pool water pH becomes unbalanced. Neutral pH is seven, on a scale of zero and 14. Levels above eight or below seven are harsh on skin and membrane tissues.
Swimmers might experience severe lung irritation if they inhale fumes from over-chlorinated pools. Over-chlorinated pools sometimes indicate poor maintenance. Improperly treated byproducts formed by the interaction of chlorine with blood or feces can create toxic conditions in the pool. One such byproduct, trihalomethane chemicals that hover just above the surface of the water, cause asthma-like symptoms and sometimes induce asthma in previously asymptomatic swimmers, according to Mary Pohlmann, assistant professor of clinical medicine at Southern Illinois University School of Medicine.
Teeth and Internal Organs
Chlorine in gas form sanitizes pools efficiently but also increases the acidity of pool water. On the other hand, high pH levels--or overly alkaline conditions--reduce the ability of chlorine to disinfect water. Adding more chlorine to pools with unbalanced pH further degrades the quality of the pool water. Highly acidic pool water can erode dental enamel. Team swimmers most often experience this damage; the more hours spent in the pool, the greater the effects of chronic exposure to acidic water. Scientists debate the potential dangers of swimmers absorbing high amounts of chlorine through the skin from chronic exposure. Chemicals pass through to small blood vessels and tissues. Concerns about links between byproducts of chlorine disinfection and bladder cancer remain unproved as of 2010.