The effects of heavy rain on a septic tank

Written by jessica kolifrath
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The effects of heavy rain on a septic tank
(Hemera Technologies/ Images)

Septic systems are tanks set underground that hold waste products as they break down into the soil. Tanks are designed to handle a specific amount of water that comes from your home, and excess water flowing into them will cause a variety of problems. This extra water can come from surface runoff created by watering your lawn, or it could be the result of a heavy or prolonged rain.

Impaired Drainage

Heavy rainfall saturates the soil around the septic tank, according to the National Environmental Services Center, preventing the water from the tank from properly draining out. Soil can only fit so much water in the spaces between grains of dirt, and, once it is saturated, the water in your septic system will stop moving. Stopping the drainage process of the tank may be fine for a day, but if heavy rains last many days, or even weeks, the tank can become full of built-up waste. The bacteria and microbes that break down solid waste in a septic system may become overwhelmed by the additional waste. Even after the water is absorbed and your tank drains again, it may take some time for the tank to process waste at full capacity again.


Septic tank backup refers to waste water that re-enters the home through a drain in a shower or sink, according to the North Carolina State University Cooperative Extension. Waste water is full of dangerous bacteria and chemicals and may cause water damage to the walls or floor of a room if it overflows.Tanks back up into the home when they are full. Extra water from heavy or extended rainfall may fill the tank up, or it may shift dirt and debris to clog the openings that let the system drain into the soil. By the time a septic tank backs up into the home, professional pumping and cleaning is required to repair the septic system.

Debris in the Drain Field

Gravel, plant material and loose dirt can be washed into the drain field of the septic tank and clog it. The experts at the University of Minnesota Extension say that this leads to backup of waste water into the home or diminished drainage. Homeowners must inspect their septic system drain field for proper drainage after a heavy rain or flooding. If the field has been clogged, a professional septic system maintenance team must repair or redesign the drain field before the tank can be used again.

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