Backwater Valves Explained
When the sewer fills during a storm, water looks for the lowest exit. A backwater valve makes sure it is not your basement.
- Plain steps you can follow before calling
- What to check, what to leave alone
- When the job needs a plumber
- Milton water, weather and housing in mind
- Licensed plumbing trade
- Booked around your day
- Price agreed before work
- Phone only, no forms
2 minute read
Written for Milton homeowners doing the first look themselves.
Have handy
- Flashlight and a bucket
- Rags or old towels
- Your main shut-off located
Stop and call when
A ceiling is dripping, a drain is pushing sewage back up, or you smell gas.
The short version
Picture a backwater valve as a flap door set into the sewer pipe leaving your house. Normally it stays open so wastewater leaves the house. If the municipal sewer surcharges during heavy rain, the flap closes and blocks sewage from flowing back into the basement. It is different from a sump pump, which handles groundwater. Many homes benefit from both. Halton Region has offered subsidies for backwater valve installation in the past; check current terms before starting.
The routine, in order
- Find out if you have one. Check the basement slab near the main drain for a round or square lid, often a round or square plastic lid.
- Learn the type. A normally open valve lets air through freely and closes only when water pushes back. That style is generally preferred over older normally closed designs.
- Inspect it. Remove the cover and look for debris holding the flap open. Wear gloves.
- Clean it. Clear any buildup gently. Follow the manufacturer's instructions; do not force the flap.
- Limit water use during storms. While the valve is closed, water from your own fixtures cannot leave. Avoid laundry and long showers during a heavy downpour.
- Plan installation properly. A new valve usually involves breaking the basement floor and requires a permit. See our pamphlet on plumbing permits for the general picture.
Mistakes to avoid
- Covering the access lid with flooring. You need to reach it.
- Installing a valve on the wrong side of fixtures, leaving some drains unprotected.
- Never inspecting it until the day it fails.
- Assuming it replaces a sump pump. It does not.
- Running the washing machine during a storm with the valve closed.
Know the difference: sewage backup comes from below through drains. Groundwater seeps in through walls and floor joints. Each needs its own protection.
Where the valve sits
The valve is installed on the main building drain, downstream of the fixtures it protects and before the line leaves the house. In most homes, that means usually close to the street side of the basement. Where downspouts, foundation drains or sump discharges connect matters too. Rainwater lines should not tie into the sanitary drain at all, and any that do should be corrected before a valve goes in.
When to ring the shop
Call us for installation, for an inspection of an existing valve, or after any backup event. A camera run of the lateral can show whether roots or a damaged pipe added to the problem. We also install and replace water heaters, and our gas water heater replacement page covers that. We work across the region, including Acton. If scale is wearing out your fixtures too, our hard water pamphlet explains why.
Questions we get asked
Is a permit required to fit a backwater valve?
Installing one typically requires a building permit and inspection. Check with your municipality.
How often should I check my backwater valve?
Lift the lid in spring and fall, and again after a big downpour.