Draining pool water into a Southlake storm drain violates city code, the city said in an advisory published Thursday, Sept. 24.

The warning targets both homeowners and pool service companies as pool season winds down. Every storm drain in Southlake flows directly into local ponds, creeks and lakes without treatment, according to the city's stormwater quality page. Chlorine, algaecide, muriatic acid and other pool chemicals can harm fish and wildlife once they reach those waterways.

Discharging pool water with chlorine above 0.1 parts per million or a pH outside the 6-to-8 range violates Chapter 9.5, Article IX of the Southlake Code of Ordinances. Dumping filter backwash into the storm system is also prohibited.

The city outlined two approved methods in an advisory on My Southlake News.

Drain through the lawn. Homeowners must first dechlorinate pool water to less than 0.1 ppm and adjust the pH to between 6 and 8. The city advises stopping all chemical treatments several days before draining and testing the water before starting. The lawn should be free of pet waste, debris and excess fertilizer, and should not have been recently treated with pesticides. Water should be pumped from the deepest part of the pool, with flow controlled to prevent erosion or runoff into the street or neighboring yards.

Use the sanitary sewer system. Residents must call Southlake Public Works at (817) 748-8082 and receive approval before using this option. The city coordinates with wastewater services to confirm the sewer system can handle the extra volume.

Both options require preparation.

The city also advises against draining during or right before rain, when the storm system already carries heavy flow. Water that still contains algaecide, muriatic acid or other active pool chemicals should never be drained, regardless of the method chosen.

Residents unsure whether their pool water is safe to drain can call the Public Works Environmental Services Team at (817) 748-8082 before starting. Suspected illegal dumping into a storm drain, ditch or creek can be reported through Southlake Serves or by calling Public Works at (817) 748-8098.