Noah had the first insurance policy against a flood – an ark

There have been a significant number of insurance water damage claims that have been denied recently, where sewers backed up into homes and caused water damage. These sewer backups were caused by a number of different issues, most of which, as you read the fine print in your insurance policy, are not covered. 

In Noah’s story, he prepared for a great flood by building an ark. When the flood came, he was prepared. The only good flood insurance we can buy is a good design to prevent water damage. If you live in a designated Federal Emergency Management Association (FEMA) flood zone, you can buy government flood insurance. But, you must first qualify by meeting the building and plumbing code requirements for buildings in flood zones.

There are many insurance claims each year for floods and water damage that are generally not covered when related to storm events. Storm events can lead to flooding when the rainfall rates exceed the drains’ ability to carry away the water. When there is a potential for storm water or sanitary sewage to back up into a building from a storm event, there should be a backwater valve installed on the building drain leaving the building, to prevent a backup of sewage into the building. A backwater valve is a device that is typically installed in the lowest portion of the building drain. It works like a check valve to prevent sewage from flowing back into the building. 

I recently visited one of the big box retailers where FEMA had a table set up to educate consumers about how to prepare for the next great flood. I thought it was a great idea because the public needs some education. The sample products they had on display were the typical internal drain type ball float and rubber bell float type backwater valves for floor drains. They also had a spring loaded check valve on the table for a sump pump discharge pipe. 

I walked up and asked the guy what the display was about, and he proceeded to show me products that could help stop a flood. He picked up a spring-loaded check valve intended for a sump pump or sewage ejector pump discharge valve, and explained how it could be installed in a drain to prevent basement flooding. He went on to explain all of the flooding in the state from the previous months heavy rains. 

I played dumb and asked what he called the device.

He said it was a “backflow preventer.”

I said, “They call that particular device a spring-loaded check valve and it is used in a pump discharge. A backflow prevention assembly is installed on a water supply pipe and a backwater valve is what you would install in the building drain to prevent backflow. That is not a backwater valve.” 

I looked around and they did not seem to have a horizontal building drain type backwater valve with a swing check valve on display. I explained that most backwater valves of the float or swing type will not prevent sewage or storm water from backing up into a building; they just slow it down. If the sewer back-up event lasts a long time, debris or sand in the valve seat can allow seepage of the waste flow back into the building.

There are many types of backwater valves. A few are shown in Figures 2 – 5. There are a few designs that have built-in shut-off valves that automatically close when the water level in the downstream sewer rises. Jay R. Smith wins my prize for the most innovative, with their flood-gate. They also have models that have a separate knife gate valve downstream of the check valve, which allows the building owner to manually or automatically close the valve to create a positive shut-off of the waste to prevent water damage on the lower floors of a building. 

If a high water alarm is installed, it can notify the owner, and/or signal a motorized valve to shut-off the water supply and a motorized waste valve when the sewers back up, minimizing the chances of flooding. If the building owner is alerted by a high water alarm, they can manually shut off the cold water supply to the building to assure no plumbing fixtures are being used, while also closing the drainage shut-off valve associated with the backwater valve. 

Many water damage cases occur where basements or lower floors of a building are located below the next upstream manhole elevation. Most insurance policies will not cover floods. So, like Noah, you have to design or prepare for the floods.

There are several terms that need to be defined when talking about building drains and sewers. The following terms are used in the model plumbing codes.

A building drain is the part of the lowest piping of a drainage system that receives the discharge from soil, waste and other drainage pipes inside. It extends 30 inches (762 mm) in developed length of pipe beyond the exterior walls of the building and conveys the drainage to the building sewer. 

A combined building drain conveys both sewage and storm water or other drainage. Note: Combined building drains within the building are generally prohibited by the codes. However, there are older existing buildings that may have combined building drains.

A sanitary building drain conveys sewage only. 

A storm building drain conveys storm water or other drainage, but not sewage.

A building sewer is the part of the drainage system that extends from the end of the building drain and conveys the discharge to a public sewer, private sewer, individual sewage disposal system or other point of disposal. 

A building combined sewer conveys both sewage and storm water or other drainage. Note: Combined sewers from a building are generally prohibited by the model codes. However, there are older existing buildings that may have combined building sewers.

A building sanitary sewer conveys sewage only. 

A building storm sewer conveys storm water or other drainage, but not sewage. 

A public sewer is directly controlled by public authority. 

A sanitary sewer carries sewage and excludes storm, surface and ground water. 

A storm sewer conveys rainwater, surface water, subsurface water and similar liquid wastes.

Sewage is any liquid waste containing animal or vegetable matter in suspension or solution, including liquids containing chemicals in solution.

There are several conditions that can contribute to water damage caused by sanitary sewer back-ups and they are as follows: 

1. Dirt, Sand and Debris in the public sewer. The debris can be caused by combined sewers that also receive dirt and sediment run-off from roadways, roofs and area drains, which can clog the pipes. New low flow legislation can also contribute to blockages because the low flow fixtures do not allow enough hydraulic depth of flow in the drain and the waste settles out in the drain and causes blockages. There is just not enough water going down the drains to move the solid waste down the drain. These blockages pile up and lead to sewer back-ups and water damage. This is becoming more frequent as water conservation is causing a dry drains phenomenon.

2. Storm water infiltration into older sewers. Storm water can enter into public sewers and building drains through poorly constructed joints in older clay or concrete sewers. Many older sewers were made of concrete, clay or brick where the groundwater can infiltrate into the sewers when there are flooding conditions. I served on my local water and sewer board, and this was a significant issue for us every time there was a storm event. 

3. Illegal sump pump connections to the Sanitary Sewer system. There have been many cases where sump pumps have been installed in basements to pump away sub-soil drainage and the discharge lines have been illegally connected to the sanitary sewer piping. During flood events and high water events, the sub soil drains contribute to a significant increase in the sewer flow with storm water. This often leads to overwhelmed sewage treatment plants and sanitary sewer overflows. 

4. Combined Storm Sewers and Sanitary Sewers. In older sections of major cities, it was not uncommon to have combined sewers from back in the days before separate sanitary and storm sewers were required. In those cities, the combined sewers have contributed significantly to sanitary sewer overflows when there is a storm event. Most combined sewers lead to waste water treatment plants in these older cities. The wastewater treatment plants are typically not sized to treat the sanitary sewer at the storm water flow rate. They are designed to handle the sanitary sewer flow rate for the connected sanitary sewer load. During storm events the storm water flow rate far exceeds the sewage treatment plants capacity, so in most cities a vault is installed on the influent line at the wastewater treatment plant that diverts the water to a holding tank or pond that is sized to handle the volume of water from a normal storm event. After the storm event, the waste is pumped through the wastewater treatment plant for treatment before being discharged to the waterway. When the sewer flow volume exceeds a normal storm event, the sewage and storm water overflows into a bypass drain around the sewage treatment plant and into the waterway where the sewage treatment plant discharges its effluent. It should be noted the effluent during a storm event is mostly storm water, but untreated sewage is bypassing directly into the waterway. Operators of wastewater treatment plants as part of their licensing requirements are supposed to document the sanitary sewer overflow events and report them to the EPA or local environmental quality authorities. 

The elevation of the top of the manhole is typically noted on the site utility drawings. The top of manhole elevation can be checked against the finished floor elevation of the building to determine if a backwater valve is required. If a sewer becomes blocked downstream of the lot can collect everything from the top of the hill until it comes flowing out of the unprotected first floor fixtures. The next upstream manhole is key, because it is the source of relief. 

The basement floor drain is typically the lowest plumbing fixture in the building plumbing system and the first to see sewage flowing from it as the public sewer backs up. The next lowest fixture may be a shower drain or water closet in the basement. The next upstream manhole might even be higher than the first floor fixture elevations. When the sewer backs up to the next upstream manhole, the sewage will lift the cover and the flow will cascade down the street.
When a sanitary sewer overflow occurs, raw sewage can flow from a manhole cover and down the street to the storm sewer and on to the nearest waterway, lake or ocean. 

If Noah was a plumber, he would design his plumbing system to address the potential for water damage in a building from a sewer backing up by installing a backwater valve on the fixtures below the first upstream manhole. The model plumbing codes require backwater valves when a fixture is installed on a floor that is below the next upstream manhole. Noah would install the backwater valve on the building drain in a location that is accessible either inside the basement or outside away from shrubs and trees. He would also bypass the backwater valve with the fixtures that are located higher than the upstream manhole so that they can still operate in the event of a back-up situation. 

Noah might also consider installing a backwater valve with a supplementary knife-gate valve to allow a positive shut-off of the sewer if the sewer is prone to potentially long periods of back-ups that can allow water to seep through a typical check valve on a backwater valve that is fouled with debris. It is important to consider shutting-off the water supply to the building during a flood event or sewer back-up event because if people are still using water in the building and the backwater valve is closed, then the waste will back up in the building drain and cause water damage from within the building. Noah would also keep all of his valuables out of the basement, so that in the event of a sewer back-up his valuables will not get damaged. 

Noah would also maintain the backwater valve on a regular basis. This requires access and cleaning of any debris caught in the check valve and lubricating valve stems and moving parts if necessary.

I hope drains always flow freely. And, if you ever get into deep water, I hope your backwater valve is working properly.

Ron George, CPD, is president of Plumb-Tech Design & Consulting Services LLC. Visit

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