What is a Drain Back Water Valve or Back Up Prevention Valve – and why do you need one?

There is nothing worse than seeing water in your basement.

Why is water coming up your floor drains? Where is it coming from? How can you make it stop?

When you take a shower, flush the toilet, or run your dishwasher, all that wastewater goes down your drain pipe and into the sewer system. It then flows into treatment plants where it is cleaned before being released into Lake Ontario.

That’s what is supposed to happen – but sometimes a heavy rainstorm, or melting snow, can cause the local sewer lines to overflow. That means the wastewater from your house has nowhere to go but back where it came from – up your drain pipe and into your house.

Fortunately you can stop sewer water from going back into your home by installing an attachment called a Back Water Valve. This valve, which is also called a Back Up Prevention Valve, Back Flow Preventer, Drain Back Up Valve, and Sewer Back Up Preventer, blocks water from coming back up the sewer line and into your house.

How a Back Water Valve works

There is a small plastic flap inside the Back Water Valve. It is normally open, which allows water to exit from your home. There are also small inflatable attachments on each side of this flap. If sewer water starts to flow back into your house, these inflatables cause the flap to raise and seal shut, preventing any water from coming in.

When the sewer water stops trying to come back into your house, the flap falls back to its normal open position, allowing wastewater to flow out of your house again.

The Back Water Valve is so important for protecting your house that most new homes have the valve installed during construction. Unfortunately homes built in Toronto before 2013 did not automatically have one installed. The good news is you can have one added to your drain system by a drain expert like Master Drain.

Installing a Back Water Valve

The first step is accessing the drain pipe at the correct location. This could be at the front of your house under your lawn or garden, or in your basement.

A section of pipe is removed to insert the Back Water Valve, and then securely sealed to your drain pipe. Master Drain then refills the area, and if a small portion of your floor had to be removed, it will be replaced. Whether it was inside or outside your house, the affected area will look the same as it did before, with the addition of a small round access port found flush to the ground or floor.

This port is used to clean the Back Water Valve and ensure it is working properly. For continued effectiveness, the manufacturer recommends that you have your Back Water Valve inspected and cleaned every year.

City of Toronto rebate

Installing a Back Water Valve takes from one to three days depending on the condition of the ground or concrete, how deep down the drain pipe is, and the availability of the city inspector. Master Drain will give you a price estimate and also arrange for any necessary permits from the city. You do not have to do any paperwork.

The City of Toronto currently offers a rebate of $1,250.00 through the Basement Flooding Protection Subsidy Program for homeowners who install a Back Water Valve. Master Drain will complete the necessary form, so all you need to do is sign and mail it in and you will receive the rebate in about eight weeks or less.

With extreme weather becoming more common in the Toronto area, a Back Water Valve is good way to protect your home. In fact, many insurance companies require you to have drain back up protection when insuring your home. It will also bring your insurance premium down.

Go to Master Drain to request an online quote today!

In early July 2013, the residents of Toronto, Mississauga, and surrounding areas got a rude awakening: the sewer and drainage systems in their homes, that in many cases had never presented a problem over decades, suddenly failed to carry off the water that was falling from the sky faster than the drains could take it away. And like water will do, it found its way to new places: up into people’s basements. As dramatic as the pictures of flooded underpasses and abandoned cars were, the real damage was less visible, and happening below grade.

So, while the roadways generally drained in a few hours, the water that risen into basements was just beginning to do its real damage. Even after it had subsided, basement floors and walls were saturated and furniture and possessions were destroyed. Mould set in, and the curbsides of neighbourhoods were lined with heaps of soaked couches and sodden rolls of carpet.
Many homes found out the hard way that their basement floor drains could work two ways: not only could they take water away from a basement floor, but they could be a conduit for water to enter a basement. Homes that had eavestrough downspouts leading water from their roofs down to drainage systems that ran beneath the basement floors were the worst affected, but even diverting downspouts did not always prevent flooding. If your downspouts were not the source of trouble, your neighbors’ or the municipal sewer might be.
More than rainwater entering through foundations or window wells, this water was quick to appear, and devastating.
So what is the way to prevent this disaster from recurring? People should realize that this “freak storm” might in fact not be a freak but the beginning of a “new normal”. Weather systems are changing, and heavy downpours are a part of that in places like Toronto. Diverting downspouts, sealing basement window wells, and ensuring watertight foundations are all good ideas, but the ultimate response to the threat of basement drain upflows is a drain backup valve.

Summer is Coming: Drain Backup Valves

What is a drain backup valve?

A drain backup valve is a valve that prevents water from backing up against the normal flow direction of the basement drain. When things are operating normally, water and waste flow from their sources into drain pipes, and then to the sewer system. In the circumstance that water is flowing the other way, a drain backup valve will shut, preventing back flow from rising up through the system.


Drain backup valves are typically installed in newly-constructed homes, but Toronto-area houses from before the 1970s did not have drain backup valves installed by default. As a result, they need to be retrofitted to the house’s drain system, a task that should be done by the experts at MasterDrain.

valve diagram

Installing a drain backup valve into an existing system involves breaking the floor slab to access the drain piping at the correct point or points, then removing a section of piping that will be replaced with the drain backup valve. Once the valve is positioned and sealed to the existing pipe, the hole is backfilled and the slab in the work area repoured. Done right, the finished project is unobtrusive, with just an access port showing, flush with the floor.

What are the advantages of a drain backup valve?


A drain backup valve provides the most reliable means of protecting basements against flooding caused by drain backups. This is important, as drain backups are usually the most damaging type of flooding. Not only does the water directly damage the basement and its possessions, but in most cases the water rising in a drain backup is contaminated with sewage, requiring many things to be discarded even if they are not irreparably damaged.

valve dimentions

In addition, many insurance companies are reluctant to insure flood-prone basements, or will require that drain backup protection be installed in order for a homeowner to qualify to re-insure their home. In those cases, a drain backup valve is not only an excellent idea, but a requirement.

Finally, as recent Toronto weather has shown, the chance of such storms and the consequent flooding is greater now than in the past, and a growing risk. Drain backup valves are future-proofing, not just waterproofing, for your basement. To add the protection of a drain backup valve to your home, contact MasterDrain.