Swimming pool water should be "safe enough to drink".

Dr. Thomas Palin is credited with inventing the DPD (diethyl-p-phenylene-diamine) method for evaluating drinking water disinfection levels. His DPD tablet method of testing water for free and combined chlorine has been approved by the U.S.EPA.

The DPD test is used to evaluate the water in most swimming pools operating today. Most regulatory agencies incorporate the DPD standards into their regulations governing public swimming pools and spas.

The subject of sanitizing your swimming pool water is more complex and detailed than can adequately be covered on this page. Therefore, a brief overview of pool chemicals and their purpose is more practical. If you are interested in a thorough discussion of swimming pool chemicals, which ones are appropriate for your specific situation and how to safely use them please click on these links: "How to Properly Maintain Swimming Pool Water Chemistry"; and "How Swimming Pools Work".

Sanitize the water.

The basic purpose for sanitizing the water is relatively simple: to remove any harmful bacteria and pathogens that may make swimmers sick, and to keep the water clean and clear. The filtering system of the pool works to remove large particles of dirt and debris from the water, while chemicals (usually chlorine or bromine) work to neutralize and remove the smaller and much more dangerous contaminants.

Chlorine.

Chlorine comes in both solid and liquid forms. Many residential pool owners use chlorine in tablet form to keep their water safe for swimming. When added to the pool, chlorine reacts with the water to form hypochlorous acid, which in turn kills bacteria and other pathogens. Unfortunately, hypochlorous acid doesn't like to stay very long in the water. It tends to dissipate in sunlight and therefore must be stabilized by the addition of another chemical such as cyanuric acid. Merely adding more and more chlorine is not the answer because too much can cause other problems (affecting bathers and the pool) without increasing the sanitizing condition of the water. The level of available or "free chlorine" in your pool should be maintained at 1-3 ppm (parts per million). The amount of chlorine in pool water is measured using a swimming pool test kit.

Bromine.

Bromine also kills pathogens, however it is most notably used in warm water situations such as spas and hot tubs. Both chemicals kill bacteria. Bromine tends to be more gentle on the skin, but bromine is normally more expensive than chlorine, making it not as cost-effective for swimming pools.

Tests.

There are primarily two types of swimming pool test kits: (a) Colorimetric test kit - a reagent is added to a sample of pool water. The resulting color is compared to a color chart that indicates the level of the specific chemical being tested; and (b) Titration test kit - an indicator reagent is added to the water sample followed by the addition of a specifically measured amount of secondary reagent. Again, the resulting color is compared to a color chart. Basically, a titration test kit is a more sensitive testing method, but both methods are valid for a residential pool. There are many brands of pool water test kits on the market. It is very important, however, that the reagents in your test kit are fresh. Old reagents may give false test results. Consult your pool supply professional for the test kit that is best for your pool.

Other factors affecting pool water that you should consider are pH and alkalinity. pH is described as the acidity-alkaline balance of a substance (in this case, pool water) and is measured on a scale of 0 to 14 with a pH of 7 being neutral. Below 7 is considered increasingly acidic whereas a pH above 7 is considered increasingly alkaline. Different types of chlorine react more effectively at different pH values (check with your pool chemical supplier). You should try to keep the pH level of the water between 7.2 and 7.8 as measured with your test kit.

pH levels can fluctuate whenever anything foreign is introduced into the water such as dirt or debris, sweat or urine, body lotions or suntan oils, etc. The "total alkalinity" level of the water tends to buffer the pH to prevent it from fluctuating wildly in order to maintain optimum water conditions. Of course, total alkalinity is another chemical level that you would want to test. Try to keep total alkalinity between 80-120 ppm.

There are other conditions affecting swimming pools that you should be aware of such as calcium hardness, total dissolved solids, and algaecides (used to control abnormal algae growth in pools).

As you can see, there is much involved in maintaining your pool water for the enjoyment of your family and friends. Successfully balancing these parameters will keep your pool clean, clear and safe. Have your pool equipment supply professional guide you in balancing the water. Also, check out this publication from the U.S. EPA on how to safely handle and store your pool chemicals: Safe Storage and Handling of Swimming Pool Chemicals.

We provide links to many other government publications on swimming pool safety. Just click here.