What Is a Sump Pump and How Does it Work?

Oct 15, 2024

Jennifer Farrington is a contributing writer at USA TODAY Homefront. She is a Florida native who has more than a decade of writing and editing experience. Jennifer has covered everything from real estate and insurance to personal finance and entertainment.

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Sump pumps collect excess water around your home’s foundation drains.

Sump pumps move excess water at least 20 feet from your home to prevent indoor flooding.

Backup sump pumps engage when your main pump fails, which can help protect your home when you lose power.

A sump pump prevents indoor flooding by collecting excess water from your home’s foundation drains and pumping it safely away from your home. It’s installed in or near a sump basin beneath your home’s foundation — either underwater or above the water line. If you live in a flood-prone area, consider factoring a sump pump into the cost of basement waterproofing.

“The primary benefit of a sump pump is to keep any area below flood rim level — such as a crawlspace, basement, or diversion pit — free of water,” explained Mike Prencavage Jr., owner and president of The Family Plumber in Los Alamitos, California.

When a sump basin fills enough, a float activates the pump to remove water through a discharge line. Some water inside the sump is normal, as it helps keep your unit cool and lubricated and prevents overheating, but too much can signal a problem such as a blockage.

If you live in an area that’s prone to flooding or frequently experiences heavy rainstorms, a sump pump can help protect your home from flooding and prevent foundation water damage.

In regions with a high water table, where the soil around your home is constantly saturated, preventative equipment, such as a sump pump, is crucial to divert excess water and keep your home dry.

“The location of your home usually dictates if and when a sump pump should be installed. For instance, a sump pump is recommended if a home is near the beach where water tables are higher or is susceptible to heavy rainstorms,” Prencavage said.

The water table is the underground boundary between the soil surface and the zone where groundwater fills the gaps between rocks and sediments.

Sump pumps come in various types, and choosing the right one depends on your home’s specific needs and the water levels in your area.

Submersible sump pumps are designed to operate underwater, at the bottom of the sump pit, making them much quieter than other types. They feature oil-cooled motors and tight seals that protect them from moisture and dust, contributing to their durability and long life span. However, this reliability typically comes at a higher cost.

A pedestal sump pump is ideal for areas with low water tables and small sump basins. Unlike submersible pumps, pedestal models sit above the water line, with the motor positioned at the top of the system, keeping it dry. This design makes them noisier but easier to access for maintenance.

While sump pumps are effective, they can fail during power outages, so having a backup is recommended. Backup pumps aren’t connected to the grid but run using hydropower or batteries. This way, you’ll have a sump pump to protect your basement or crawl space even if hazardous weather cuts electricity to your home or neighborhood.

Water-powered sump pumps are commonly used as a backup system. For example, the City of Sioux Falls strongly recommends these as a precaution for homeowners in the area. These pumps automatically kick in if the primary pump fails or shuts down due to a power outage, increasing the likelihood your basement or crawl space stays dry during emergencies.

Battery-operated sump pumps are essential backups that operate when your primary pump fails due to power outages. These pumps get power from a battery pack, which will eventually need recharging or replacement.

Battery-powered models can run for around 100 hours or more, giving you a few days to arrange for repairs to your main sump pump. These systems typically include a limited warranty, offering extra peace of mind.

Primary sump pump systems are your best defense against basement flooding and flood damage. They work by actively removing excess water from the sump pit, keeping your basement dry and safeguarding your home’s foundation. By doing so, sump pumps help prevent mold, mildew and other moisture issues from excess water.

“Sump and pumping systems are beneficial in the discharge of effluent or storm water when the building sewer or building storm sewer is incapable of draining by gravity,” explained Carlos Flores, the Division Manager of Plumbing Inspections at the City of Houston.

A sump pump is essential for maintaining a dry, safe environment for homes with finished basements or valuable items stored below ground.

A sump pump is placed in a pit at the lowest point of the basement floor. Whether submersible (at the pit’s bottom) or pedestal (beside the pit), it collects groundwater from rain and snowmelt. Water enters the pit via pipes called the footing drain and inlet pipe. When the water level rises, a float mechanism activates the pump, expelling excess water away from your home through a discharge pipe, also known as a sump pump outfall.

Sump pumps should be connected to the stormwater collection system or drain onto your lawn, where water can flow into a ditch or gutter, according to the City of Sioux Falls. While codes vary by city and state, most jurisdictions prohibit homeowners from connecting a sump pump to the sanitary system, such as a floor drain, toilet or sink, as it’s not designed to handle the additional flow.

The discharge point should be at least 20 feet away from your home, according to The International Association of Certified Home Inspectors (InterNACHI). If the sump pump discharge pipe releases water too close to your home, it can be recycled back into the sump basin, reducing its effectiveness and potentially overloading the system. Draining onto a lawn, however, prevents issues such as sidewalk icing in winter or slippery algae in summer, and it avoids becoming a nuisance to neighbors.

The float switch in the sump pump pit functions as a sensor. When the water level reaches a certain threshold, the float switch activates the pump, draining water away from your home.

Electronic switch: An electronic switch triggers sump pump activation using tiny electric currents. When the probes in the sump pit touch the water, they complete an electrical circuit. The switch then measures the water’s electrical resistance and turns on the pump when it detects the water level is high enough.

Tethered float switch: A tethered float switch is the most common type. It has a hollow float with a steel ball inside, connected to the pump by a cord. As the float rises with the water level, the steel ball moves and triggers the electric switch.

Vertical float switch: Vertical float switches usually feature a floating mechanism linked to a rod on the switch. The float rises as the water level increases, pushing the rod to engage the switch. This design is ideal for shallow, small basins.

Diaphragm pressure switch: Though not a float switch, the diaphragm pressure switch serves a similar purpose. It uses the pressure from the incoming water to trigger and activate the pump.

Most homes with basements have a sump pump. If you’re unsure whether your home has one, “start at the circuit breaker box and look for a switch labeled “sump pump.” By code, these pumps must be on their own dedicated breaker,” Prencavage said.

Flores also suggested looking for signs of an existing sump pump or system, such as a buried tank, electrical wiring or an alarm panel in the basement or elsewhere on the property. If there’s no obvious indication, a professional plumbing contractor can help you determine if a sump pump system is installed.

The average cost to install a sump pump typically ranges from $1,500 to $3,000 for parts and labor, according to Prencavage.

Beyond the initial purchase and installation costs, ongoing maintenance will help keep your sump pump operating effectively and prevent corrosion. You should have your sump pumps serviced annually and when selling your house, according to InterNACHI.

While most homeowners can likely manage routine tasks such as cleaning the inlet screens, those unfamiliar with plumbing systems may need to hire a professional for regular maintenance.

If your home already has a sump pump, consider investing in a battery backup system for emergencies that knock out power — this will also provide you with a buffer to schedule repair or replacement if your main pump fails.

If you’re unsure whether your home has a sump pump or if sump pump installation is needed to prevent basement or crawl space flooding, research and hire a reputable, licensed plumber with a history of satisfied customers. We recommend gathering and comparing at least three quotes before making a hiring decision.

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Jennifer Farrington is a contributing writer at USA TODAY Homefront. She is a Florida native who has more than a decade of writing and editing experience. Jennifer has covered everything from real estate and insurance to personal finance and entertainment.

Mike Miller is an editor for USA TODAY Homefront, covering topics that range from moving to gutters and gutter guards. He lives in North Carolina, but as a Minnesota transplant he has firsthand knowledge of long-distance movers’ pain points. Mike has written about home and life insurance providers for Marketwatch, This Old House and Architectural Digest. He also edited three national consumer magazines about natural health and wellness — Alternative Medicine, Eating Naturally and Natural Solutions. He has a BS in creative advertising with a certificate for technology, arts and media. In his spare time, Mike rides his motorcycle, plays with his two cats and spends time with his wife and twins.

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