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Keeping Prescription Medications out of the Water Supply

Post Date:06/01/2015 8:00 AM

We recently received a question from a concerned citizen asking why people should not dispose of prescription drug medications down the sink or the toilet.


How can disposing of prescription drugs down the drain cause groundwater pollution?

Gilbert receives the wastewater from homes and businesses in our enclosed sanitary sewer system and delivers it to either of our two wastewater reclamation facilities. The water is then filtered, denitrified, and disinfected so that it can be safely reused. Gilbert uses this reclaimed water directly for irrigation of parks, HOA landscapes, and golf courses.

We also recharge reclaimed water into the aquifer, to help increase the groundwater levels beneath Gilbert. Groundwater is a buffer against drought if surface water supplies are ever reduced.

In Gilbert, recharge occurs at:

1.     The Riparian Preserve (located southeast of Greenfield and Guadalupe Roads)

2.     The south recharge facility (located northeast of Higley and Ocotillo Roads)

3.     The Neely recharge facility (located northeast of Cooper and Elliot Roads)

4.     An injection well facility


The reclaimed water sent to Gilbert’s recharge facilities is Class A+ reclaimed water. Reclaimed water that is recharged at these sites can be withdrawn at a later date using recovery wells. 

The recharge basins at the facilities listed above cycle through periods of filling and drying. The process of percolating the reclaimed water through the saturated zone, vadose zone, and eventually into the aquifer is called Soil Aquifer Treatment. Any solids or pathogens in the reclaimed water are removed in the upper layer of soil, or the first 100 feet of the recharge basin. Large molecules simply will not pass through the tight spaces in the soil all the way down to the aquifer.


The wetting and drying process of the percolation basins promotes aerobic bacteria near the soil’s surface. These bacteria biodegrade (thus remove) some of the remaining solids or pathogens in the reclaimed water.

Although the reclaimed water that Gilbert uses to recharge the groundwater aquifer is filtered, denitrified, and disinfected, and then further treated through the Soil Aquifer Treatment mentioned above, it is possible that chemical components of prescription medications can still be found.


Therefore, we must do all that we can to prevent pharmaceuticals from entering our sewer system, which will help keep it out of the environment. Consider also that the recharge basins found throughout Gilbert have become home to many types of wildlife. The presence of pharmaceuticals in these waterways should be prevented for all of us—people, wildlife, and the environment.

How should I dispose of my prescription drugs?

The Gilbert Police Department houses a drop box for prescription and over-the-counter drugs in the lobby of the main station at 75 East Civic Center Drive.  This drop box was set up in order to keep these harmful chemicals out of our children's hands and keep our environment chemical-free. It is available 24/7. You can find more information here.


Acceptable items include: Prescription drugs, prescription patches, prescription samples, pet medication, and over the counter medications including vitamins.

Taking proper action to dispose of prescription medications ensures a safe and reliable water supply and environment for all Gilbert residents.