How WaStop® Inline Check Valves Prevent Basement Flooding

What Causes Basement Flooding Through Drains?

When heavy rain overwhelms the sewer network, water has nowhere left to go — except backwards through the pipes. In a combined sewer system, where surface water and foul sewage share the same pipes, this overflow can back up through the lowest drainage point in your home. For properties with basements, that lowest point is almost always the basement floor drain or ground-floor WC.

This kind of flooding — called drainage backflow or sewer surcharge flooding — is becoming more common as urban surface water runoff increases and sewer infrastructure ages. It can happen in minutes, with no warning, and the damage from contaminated water is often severe and expensive.

How WaStop® Inline Check Valves Work

The WaStop® Inline Check Valve is a passive, automatic backflow prevention device that sits inside your existing drainage pipework. It requires no electricity, no manual operation, and no ongoing maintenance.

The principle is straightforward:

• Under normal conditions, the valve opens freely, allowing wastewater and surface water to flow out of the property as usual.
• When flow reverses — as it does during a sewer surcharge event — the valve automatically closes, sealing the pipe and preventing water from entering the property.
• Once the surcharge pressure subsides and normal flow resumes, the valve reopens without intervention.

Unlike traditional flap valves or mechanical non-return valves, the WaStop® uses a flexible sleeve design that creates a reliable, watertight seal under backflow pressure. There are no moving parts that can corrode, jam or fail in the closed position.

Is WaStop® Right for Your Property?

WaStop® is suitable for any property where flooding could enter through a drainage connection. It is particularly well suited to:

• Properties with basement or lower-ground-floor drainage connections
• Homes on low-lying ground or in flood-risk catchment areas
• Properties served by combined sewer networks (where surface water and sewage share the same pipe)
• Any building that has previously experienced drainage backflow flooding

WaStop® is available in pipe diameters from DN/OD 100mm up to DN/OD 800mm, making it suitable for residential drain connections, commercial premises and municipal pipe networks alike.

Installation: Simpler Than You'd Expect

One of the key advantages of the WaStop® Inline Check Valve is how straightforward it is to install. Because it fits inside the existing pipe, there is no need for excavation, concrete breaking or structural work. A qualified drainage contractor can typically complete a residential installation in a matter of hours.

The valve is inserted through an access chamber or inspection cover and positioned at the appropriate point in the drainage run — usually just downstream of the property boundary, before the connection to the public sewer. Once installed, it is completely passive: there is nothing to switch on, adjust or service.

NordSeal can advise on the correct product size and specification for your drainage system and, where required, can recommend experienced installation contractors.

What Happens Without Protection?

At Tofta in Lidköping, Sweden, a residential pump station had been relying on a manually-operated overflow valve to prevent backflow. The valve required regular inspection visits — and when those visits were missed or delayed, the result was basement flooding for local residents. After installing a WaStop® DN315, the manual oversight was eliminated entirely. There have been no flooding incidents since, and residents now have the peace of mind of a system that works automatically, every time.

That kind of reliability is what the WaStop® is designed to deliver — whether protecting a single home or an entire drainage network.

The Cost of Not Acting

Flood damage from contaminated water is categorised as a major insurance claim. Clean-up, structural drying, replacement of flooring and contents, and temporary rehousing costs can run into tens of thousands of pounds for a single event. Many insurers also increase premiums significantly after a flooding claim, or exclude drainage flood cover altogether.

Compared to those costs, a properly specified and installed WaStop® valve is a modest, one-time investment in long-term protection.

Get the Right Advice Before You Buy

Selecting the right valve size and installation point matters. An undersized valve can restrict normal flow; an incorrectly positioned one may not provide full protection. NordSeal's technical team is available to assess your drainage layout, recommend the right product, and ensure your installation provides the protection you need.

Browse the full WaStop® Inline Check Valve range — available in DN/OD 160 to 800 — or contact our technical team for free advice on which size is right for your drainage layout.