First Flush Diverters: Do They Really Improve Water Quality?

What Are First Flush Diverters?

First flush diverters are devices installed on the roof gutter outlet that redirect the initial flow of water from the roof, known as the “first flush,” into the storm drain or a separate diversion pipe. This first flush typically contains a high concentration of debris, sediment, and contaminants that have accumulated on the roof. By redirecting this water, the first flush diverter ensures that cleaner water enters the storage tank.

How Do First Flush Diverters Work?

A typical first flush diverter consists of a valve or a floating device that is triggered by the flow rate of the water. When the initial flow rate exceeds a certain threshold, usually around 1-2 gallons per minute, the valve opens, allowing the first flush to be diverted away from the storage tank. The threshold value depends on the specific design and installation of the first flush diverter, but 1-2 gallons per minute is a commonly used value. Once the first flush has been diverted, the valve closes, and the remaining water flows into the storage tank.

Benefits of First Flush Diverters

First flush diverters offer several benefits, including improved water quality, reduced maintenance, and increased storage tank lifespan. By removing debris and contaminants from the water, first flush diverters prevent clogging and damage to the storage tank and piping. Additionally, first flush diverters can reduce the risk of waterborne pathogens and other contaminants entering the storage tank, making the water safer for drinking, cooking, and other household uses.