Sump pumps discharge water to one of four places: the storm sewer, the sanitary sewer, the ground surface near your home, or a dry well buried underground

The discharge location depends on your local plumbing code, your home's location, and what drainage systems exist beneath your street. Most homes in urban and suburban areas pump to either the storm sewer or sanitary sewer. Homes in rural areas or places without municipal sewers often discharge to the ground surface or a dry well. The wrong discharge method can create flooding problems for neighbours, violate local code, or cause your pump to back up into your basement.

Your discharge pipe leaves the sump pump basin, travels horizontally or upward through your basement wall or foundation, and then either connects to an underground pipe system or releases water above ground. The pipe is usually 1.5 inches in diameter and includes a check valve to prevent water from flowing backward into the pump when it shuts off.

Key Takeaways

  • Storm sewers are the most common discharge point in cities and suburbs, and they are designed specifically to handle large volumes of water during rain.
  • Sanitary sewers should only receive sump pump water if your local code permits it, because they are meant for household waste and can overflow during heavy rain.
  • Surface discharge and dry wells are typical in rural areas without municipal sewers, but surface discharge requires the water to drain away from your foundation and neighbours' property.
  • Your discharge pipe must include a check valve to stop water from flowing backward into the sump basin when the pump is off.
  • Connecting to the wrong sewer system or discharging water toward a neighbour's property can result in code violations and costly repairs.

Storm sewer discharge: the most common option

The storm sewer is a separate underground pipe system designed to carry rainwater and groundwater away from homes and streets. It does not carry household sewage. If your city has a storm sewer system, your sump pump discharge pipe connects to it either directly or through a catch basin in your yard. This is the preferred discharge method in most municipalities because the system is built to handle the volume of water a sump pump produces.

To connect to the storm sewer, your discharge pipe runs from the pump, through your basement wall, and either into a buried pipe that leads to the street or into a catch basin (a small underground box with a grate on top). The connection point is usually marked on your property or visible as a metal grate in your yard or driveway. If you are unsure whether your home has a storm sewer connection, contact your city's public works or water department — they can tell you which sewer system serves your address and whether a storm connection already exists.

Storm sewers are separate from sanitary sewers in most modern cities, but in older cities the two systems are combined. If your area has a combined sewer system, discharging a sump pump into it can cause the system to overflow during heavy rain, which sends untreated sewage into rivers and streets. Your local code will tell you whether you can use the storm sewer or must choose another option.

Sanitary sewer discharge: only where code allows

The sanitary sewer carries household wastewater from toilets, sinks, and showers to a treatment plant. Some municipalities permit sump pump discharge into the sanitary sewer, but many do not. Discharging large volumes of water into a sanitary sewer during heavy rain can overwhelm the system and cause backups into homes or overflows at the treatment plant. Check your local plumbing code or contact your city's water department before connecting a sump pump to the sanitary sewer.

If your code does permit sanitary sewer discharge, the connection is made at a cleanout (a capped pipe that provides access to the sewer line) or at a designated point inside your basement. The discharge pipe connects with a tee fitting so water flows into the sewer line without blocking it. A check valve is essential to prevent sewage from backing up into your sump basin.

In areas with combined sewers, sanitary sewer discharge is usually prohibited because it adds to the overflow problem. Even where it is permitted, many municipalities are moving away from allowing it in order to reduce strain on treatment plants during storms.

Surface discharge: water released above ground

Surface discharge means the sump pump pipe exits your home above ground and releases water onto the soil surface. This method is common in rural areas without municipal sewers and is permitted in many suburban areas as long as the water drains away from your foundation and your neighbours' property. The discharge point is usually a short length of pipe that extends a few feet from your basement wall, or a pop-up emitter (a valve that sits flush with the ground and opens when the pump runs).

For surface discharge to work, the ground must slope away from your home so water flows downhill and does not pool against your foundation or run toward a neighbour's basement. If your yard is flat or slopes toward your home, surface discharge will not work — water will either seep back into your foundation or flood your neighbour's property. In those cases, a dry well or connection to a municipal sewer is necessary.

Surface discharge is the least expensive option because it requires only a short pipe and no connection to an underground system. However, in winter, water discharged above ground can freeze and block the pipe, which can cause the pump to back up into your basement. Burying the discharge pipe below the frost line (the depth at which soil does not freeze) or using a pop-up emitter that sits above ground prevents this problem.

Dry wells: underground water storage

A dry well is a buried pit or chamber that collects water from the sump pump discharge pipe and allows it to soak into the ground. It is used when surface discharge is not possible (because the yard does not slope away from the home) and a municipal sewer connection is not available. The dry well is typically a large plastic basin or a hole lined with gravel and landscape fabric, buried 4 to 8 feet from your foundation.

The sump pump discharge pipe runs from the pump, through your basement wall, and down into the dry well. As water enters the well, it soaks through the gravel and into the surrounding soil. A dry well works only if the soil drains well — clay soil or soil with a high water table will not drain fast enough, and the well will fill up and overflow. Before installing a dry well, have a percolation test done to confirm the soil can absorb water at the rate your pump produces it.

Dry wells are more expensive than surface discharge because they require excavation and materials, but they are cheaper than connecting to a municipal sewer. They also solve the freezing problem because the pipe is buried below the frost line. However, they require more maintenance — the gravel and landscape fabric can clog over time, and the well may need to be pumped out or rebuilt after several years.

Check valves and backflow prevention

Every sump pump discharge pipe must include a check valve, a one-way valve that allows water to flow out of the pump but prevents it from flowing backward into the basin. Without a check valve, water in the discharge pipe will drain back into the sump basin when the pump shuts off, which wastes energy and can cause the pump to run more often than necessary. In freezing climates, backflow can also cause water to freeze in the pipe and block the discharge line.

Check valves are installed in the discharge pipe as close to the pump as possible, usually within a few feet. They are straightforward devices with a flapper or ball inside that opens when water flows out and closes when pressure reverses. Over time, check valves can become stuck or clogged with sediment, which reduces their effectiveness. If your sump pump runs but water does not discharge, or if water drains back into the basin after the pump shuts off, the check valve may need cleaning or replacement.

Local code requirements and permits

Your local plumbing code specifies where sump pump water must be discharged and what materials and methods are required. Some codes require a permit before installation, while others do not. Before you install a sump pump or change the discharge location, contact your city or county building department to learn what is required in your area. They can tell you which discharge methods are permitted, whether a permit is needed, and what inspections are required.

Code requirements vary widely. Some municipalities require discharge to the storm sewer if one exists, while others permit surface discharge as long as the water drains away from the foundation. Some prohibit sanitary sewer discharge entirely, while others allow it under specific conditions. Rural areas often have no requirements because there is no municipal sewer system, but even there, discharging water toward a neighbour's property can create a legal liability.

If you are unsure about your current discharge setup, or if you are planning to install or modify a sump pump, contact your local building department or a licensed plumber who knows your area's code. Installing a sump pump that violates code can result in a citation, an order to change the discharge location, or liability if water damage occurs to a neighbour's property.

Frequently Asked Questions

Can I discharge my sump pump into the sanitary sewer?

It depends on your local code. Some municipalities permit it, but many do not because large volumes of water can overwhelm the treatment plant during storms. Contact your city's water department or building inspector to find out what is allowed in your area. If your area has a combined sewer system, sanitary discharge is usually prohibited.

What happens if my sump pump discharges toward my neighbour's property?

You can be held liable for water damage to their foundation, basement, or landscaping. Even if your local code does not explicitly prohibit it, discharging water toward a neighbour's property is a common source of disputes and lawsuits. The discharge pipe must direct water away from all neighbouring properties and toward a drainage system or a slope that carries water away from homes.

Can I discharge my sump pump into a storm drain on the street?

Only if your local code permits it and the storm drain is designed to accept sump pump discharge. Some municipalities allow direct connection to street storm drains, while others require the discharge to connect to the municipal storm sewer system through an underground pipe. Contact your public works department to find out what is permitted in your area.

What should I do if my sump pump discharge pipe freezes in winter?

Bury the discharge pipe below the frost line (the depth at which soil does not freeze in your area) so water does not freeze inside it. If the pipe is above ground, insulate it or use a pop-up emitter that sits flush with the ground. If the pipe is already frozen, pour warm water down the sump basin to melt the ice, or use a heat tape wrapped around the exposed pipe.

How do I know if my sump pump is discharging properly?

Watch the discharge pipe during a heavy rain or when the pump runs. Water should flow steadily out of the pipe and away from your home. If water does not discharge, the check valve may be stuck, the pipe may be clogged, or the pump may not be working. If water drains back into the basin after the pump shuts off, the check valve is not sealing properly and needs to be cleaned or replaced.