Swimming Pools

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The water in swimming pools must be treated with chlorine to kill possible pathogens and protect human health. Even at extremely low levels, chlorine can be toxic to aquatic animals and plants. When draining a pool, the water must be discharged to the public sewer not to a storm drain.

  • Storm drains are a direct conduit to nearby streams.
  • Chemicals poured down storm drains flow to the nearest stream and can have an immediate adverse impact on stream water quality.
  • Chlorine and other pool chemicals, including cleaning compounds, negatively impact plant and aquatic life in our streams.
  • The streams in Montgomery County discharge to rivers that drain to the Chesapeake Bay. Pollution in our local streams and rivers impacts the health and vitality of the Bay.

Do you own, operate, or maintain a swimming pool?

  • For owners and operators of community pools and swim clubs: 1) Pool water, backwash water, and wastewater discharged to a sanitary sewer should pass through a surge tank, 2) Pool water, backwash water, and wastewater discharged to a storm drain or stream requires a General Discharge Permit from the Maryland Department of Environment (MDE) and the criteria listed below must be followed. For more information about General Discharge Permits call MDE at (410) 537-3323 or visit their website.
  • For residential pools served by less than four homes: a permit is not required to discharge pool water, backwash water, or wastewater but the criteria listed below must be followed.

Guidelines for discharging pool water, backwash water, and wastewater to streams and storm drains

  • Maryland State law prohibits the discharge of chlorine or chlorine products into streams that exceed 0.1 ppm chlorine. Chlorine can be tested using a standard pool chlorine test kit. (Bromine can have the same impacts on aquatic life and should be handled in the same manner.)
  • The pH, which is a measure of acidity, of the pool water, backwash water, and wastewater must be between 6 and 9 prior to or during discharge. Cleaning fluids and compounds, such as muriatic acid (which is toxic to aquatic life) can lower the pH in the water. The water must be neutralized before discharging.
  • Cyanuric Acid is used in outdoor pools to reduce the loss of residual chlorine from ultraviolet light. The Cyanuric Acid concentration in pool water, backwash water, and wastewater is limited to a daily maximum of 100 mg/L during discharge.
  • Algaecides, used to eliminate algae in pool water, can severely interrupt normal algal and plant growth in our streams. As such, the use of algaecides containing metals, such as copper or silver, is discouraged and must meet requirements if discharged. “If the label contains a warning against discharging water treated with the algaecide into lakes, streams, ponds or other water bodies, the algaecide may not be used.”
  • Total suspended solids (TSS), which are a measure of visible particulates suspended in water, must be below a daily maximum of 60 milligrams/liter (150 NTU). To achieve this level of clarity in pool water, allow suspended, visible particles, to settle out of the water. In other words, the water should appear clear. (Materials which settle out should not be discharged into streams.)
  • If discharging into the environment is your only option, direct the flow onto the land surface, since absorption into the ground offers some opportunity for chemical pollutants to react with subsurface soil, thereby filtering the water. Allow the discharge to flow slowly over the land surface to provide an opportunity to reduce water quality impacts. Overland discharges must still meet the conditions outlined above, since chemicals in the water may harm grass and plants. In addition, minimize temporary flooding and erosion when draining pools by discharging the water gradually. You must control the water flow across your property to avoid erosion and prevent a nuisance condition for neighboring properties.

What You Can Do:

Use the following guidelines when discharging swimming pool water:

  • Pool water must sit for at least 48 hours after the addition of chlorine, or until the chlorine level is below 0.1 milligrams/liter. Chlorine concentration should be tested using a standard pool chlorine test kit prior to discharge.
  • The pH of the pool water must not be less than 6.5 or greater than 8.5 at the time of discharge.
  • The pool water must be free of algaecide at the time of discharge. Algaecide can severely affect normal algae and plant growth in streams.
  • The water should not look murky or cloudy. Solids suspended (or particles) in the water must be below 60 milligrams/liter. The best way to achieve this level of clarity is to allow visible particles to settle out of the water. The material settled out should not be discharged with the water.

For community pools in areas served by public sewer, pool water must be discharged to the public sewer and must not be discharged to a storm drain. For residential pools, backwash water must be discharged to the public sewer. If your only option in draining pool water is to discharge directly into the environment, the water being discharged must comply with the State of Maryland Water Quality Criteria.