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Web Exclusive - October 2015

Eco-Friendly Swimming Pool Draining

By Terry Arko


When drained for closing and cleaning, swimming pools can, unfortunately, become a contributor to the pollution and degradation of our waterways and oceans. As pool professionals and recreational facilities with swimming pools, we are all aware that it is imperative to make every effort possible to minimize the pool's environmental impact, especially when releasing water during draining. Here are some friendly reminders about the effects of pool draining and tips to ensure we all use "best practices" to minimize the impact on the environment while simultaneously conserving water.

Nutrient Overloading

When lakes, rivers and streams become overwhelmed with the byproducts of increased agriculture and industry, the result is an influx of algae-enriching nutrients, such as nitrogen and phosphates. Phosphates are a primary growth nutrient for algae, and when there is abundance in the waterways, excessive algae results. When an overabundance of algae occurs, dissolved oxygen levels decrease and fish begin to die. When this nutrient-rich water reaches oceans via streams and rivers, it causes persistent red tides made of toxic algae that kill marine mammals and fish, and can cause respiratory illness in humans who come in contact with the algae.

One vivid example of nutrient overloading is the prolific algae bloom that clogged the 2008 Olympic sailing venues off the coast of Qingdao, China. The blooms occurred in a heavily industrialized region of the Yellow Sea where untreated sewage from coastal cities and high levels of nitrates from agricultural and industrial runoff feed into the sea.

According to the U.S. Geological Survey, 80 percent of the earth's surface is water. Ninety-seven percent of the water on earth is saltwater in oceans and seas. Three percent of the water is fresh, and only 1 percent of that is available for use. The problem is that today much of the water available for use is threatened by "nutrient overloading."

Environmental experts agree that the only way to solve the increasing algae problems is to limit the nutrient pollutants entering our lakes, rivers and streams.

Pool Chemicals' Effect on the Water System

It's important to understand the impact swimming pools can have upon the earth's water. When backwashing or draining, whatever is in the water eventually gets deposited into waterways. The following list is an example of what can end up in the water system when pools are drained:

  • Chlorine
  • Phosphates
  • Nitrates
  • Calcium hardness
  • High TDS
  • Bacteria and protozoa
  • Acidic water
  • Salt

All of these, individually or combined, can have a vast impact upon the environment, leading to possible fish kills, excessive algae, increased salinity and overall harm to the water. Because of this, many state and local environmental agencies regulate how, when and where swimming pools can be drained. It is the pool professionals' responsibility to know the local regulations for pool draining. Many areas have strict requirements for lowering chlorine levels and buffering acidic water. Others do not allow draining into storm drains or gutters. There are even some requirements that forbid pool water from touching any properties other than the property where the pool is located.

Salt Systems, Special Practices

Many pools are now using salt chlorine generator systems to sanitize. Pool pros should always do their homework and check the regulations for draining these types of pools. Some areas forbid the draining of salt generator pool water into their system. For example, Santa Clarita, Calif., was one of the first areas to develop a law forbidding the draining of salt generator pools into the sewer to prevent an increased level of salinity in the Santa Clara River.

Eco-Friendly Recommendations

When preparing to drain a pool, the first step is to evaluate the condition of the water. Is the water properly balanced? Has the pool been properly sanitized, or is it a swamp? Is the chlorine high? Does it contain high levels of metals or salts? Has it been tested and treated for phosphates?

  1. Superchlorinate/Shock: If the water hasn't been sanitized recently or is in a swamp condition, then the pool should be superchlorinated to deal with bacteria, algae and organic matter. If draining to the sewer is permitted, you may not need to superchlorinate, as the water will be treated at the municipal plant. If you do superchlorinate to clean up the pool before draining, you should try to get the chlorine to 30ppm and hold it for 12 hours. This will inactivate most bacteria and protozoa that can be present.
  2. Dechlorinate: Before draining, the water should be dechlorinated. The best way to achieve this is to allow several days before draining so the water can lower the chlorine level naturally. If this is not possible, the pool can be dechlorinated using sodium thiosulfate.
  3. Treat for phosphates: Once the pool has been dechlorinated, you should test for phosphates and, if needed, treat to lower the phosphates to at least 200ppb before discharging. As mentioned earlier, phosphates are a prime pollutant to our waterways and are responsible for numerous algae outbreaks in lakes and streams. Treating for phosphates is a simple eco-friendly practice that will help minimize a pool's environmental impact during draining.
  4. Filter: After treating for phosphates, the pool should be treated with a good natural-based clarifier and filtered for at least 24 hours. Look for products that are oil-free and non-synthetic.
  5. Drain: Once it is time to drain, check the hydrostatic pressure. Before draining, make sure the pool has a hydrostatic relief valve that relieves pressure from possible ground water. At a minimum, you should always know what the water table level is for the particular area in which you are draining. Failure to check this could lead to literally popping the pool out of the ground. This can cause major damage and expense. If you are not able to drain to the sewer, consider draining in a grassy area such as a field, as this will provide natural filtration to remove many chemicals and nutrients that may still be present in the water.
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