Medications and Your Septic System

By Janelle Eggert and Sara Heger

The Problem with Medications and Septic Systems

Medications are a part of daily life for many people. Have you thought about how your medications may affect your septic system and the treatment of wastewater? Normal use of many medications including over the counter drugs will not harm your septic system. However, antibiotics and certain strong medications such as those used in chemotherapy can affect the operation of your system.

High concentrations of antibiotics or chemicals can kill or retard the growth of the bacteria in your septic tank and soil treatment area (drainfield or mound). These bacteria are necessary for proper operation of your system because they digest some of the organic matter entering the tank. They reduce the amount of solids in the tank and reduce the biochemical oxygen demand (BOD) of the effluent—the water leaving the tank to the soil treatment area. If the tank bacteria are destroyed, solids accumulate in the tank much faster and can create problems in the soil treatment area.

Steps You Can Take

If you expect to be taking medications on a long or short-term basis, there are some things you can do to protect your septic system and groundwater. The human body does not completely metabolize medications, so they enter septic systems unavoidably through our body wastes. Certain medications may cause premature failure of your septic system.

Do not flush leftover medications into your septic system. High concentrations of antibiotics will destroy the beneficial bacteria. There is also potential for medications to contaminate groundwater, as a septic system may not adequately remove them from the wastewater. Some pharmacists will dispose of the medication for you if you return it to them.

There are many possible solutions to deal with medication use and septic systems. They start with simple techniques, but get more sophisticated as the problem increases.

  1. Minimize the use of antibacterial soap, cleaners and bleach, as these products further stress the bacteria in the system.
  2. Increased maintenance of your system may be required if you are taking certain strong medications, such as chemotherapy drugs. Your tank may have to be pumped more often to remove solids that are accumulating rapidly due to the loss of beneficial bacteria. Your septic professional can monitor your system and take samples of BOD or TSS (total suspended solids) and recommend a management plan.
  3. If your septic tank gets too toxic, it may be necessary to use your tank as a holding tank during a prescribed treatment.
  4. Fill the septic tank with clean water after pumping to dilute the concentrations of the medicines at the restart of the system.
  5. Certain design changes may be necessary to protect your drain field. These changes could include adding an effluent screen, which is placed on the outlet of the septic tank to limit solids exiting the tank. The effluent screen will need to be cleaned frequently if the septic tank is upset. An alarm is a critical part of an effluent filter installation as it will indicate when the filter needs to be cleaned.
  6. An effluent screen is particularly helpful if you expect a lot of hair loss; prevent hair from being washed into the septic system. It can remain suspended in the wastewater and get carried to the drain field, where it could plug the soil and cause drain field failure.
  7. Adding additional septic tanks or a pretreatment device are other possible design changes. 


University of Minnesota Extension

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