Do I need a backflow device on my water meter? Probably
Backflow prevention devices are not a new thing. In the irrigation industry it is widely known that if you are hooking an irrigation system to a potable (drinking) water supply you should install a backflow prevention device at the point of the irrigation connection.
There are a lot of rules (that can be found in your states/countries plumbing regulations) around how to choose and install a backflow prevention device to your irrigation system. As a rule of thumb this is how I choose what backflow device to use
1. Low hazard device (like an untestable dual check valve)
- I would use it on any standard domestic irrigation system.
- I would never use this device on a commercial irrigation system.
- I would never use this device if the domestic system had multiple alternate water sources that interconnected the irrigation system between a harvested/alternate water supply and a potable (drinking) water supply. Or if the irrigation system had any form of chemical injection
2. Medium hazard device (Like a testable double check valve)
- I would use this as a minimum requirement for a standard commercial irrigation system
- I could use it in a domestic situation (on occasion)
- I would never use this device if the commercial system had multiple alternate water sources that interconnected the irrigation system between a harvested/alternate water supply and a potable (drinking) water supply. Or if the irrigation system had any form of chemical injection
3. High Hazard Device (Like an RPZ backflow device)
- I would use this in a domestic OR commercial situation if the irrigation system had multiple alternate water sources that interconnected the irrigation system between a harvested/alternate water supply and a potable (drinking) water supply. Or if the irrigation system had any form of chemical injection.
- I may also use this device if a requirement for connection from a water authority was the installation of an RPZ. Many water authorities now require an RPZ backflow device as a minimum requirement if there is recycled water and potable water supply onsite.
- If there is a recycled water meter onsite and a potable water meter onsite you CANNOT cross-connect between the 2 supplies even with the use of a high hazard backflow device.
Also, many people do not know, but some available drip lines on the market use root inhibiting chemicals that have been impregnated into the dripper. In many situations, if you choose to use this dripline, you would have to use a high hazard backflow device at the point of irrigation connection
When you may need a second backflow device
On some occasions, a water authority will have a requirement to match the highest risk backflow device onsite with the backflow device at the water meter
Essentially, if you have a zone protection backflow device onsite, the water authority may require you to install a containment protection backflow device directly downstream of the water meter. The purpose of the containment device is to provide an extra level of protection to the town/water authority supply
Let me give you an example of this
You go to an existing established school to install an irrigation system to a footy oval at the rear of the school. The water meter enters at the front of the school. The water meter does not have a backflow prevention device.
At the rear of the school adjacent to the footy oval,
there is a potable water supply that is fed by the water meter (that is located at the front of the school). The supply at the rear of the school is adequate (pressure and flow wise) to feed the irrigation system. You decide you will hook into the water supply adjacent to the oval to feed the irrigation system. You have also decided that a medium hazard backflow device (Double testable check valve) is required to meet your obligations for backflow prevention of the irrigation system.
STOP AT THIS POINT
Remember the water meter had no backflow prevention device on it. You may need to install a containment prevention device directly downstream of the water meter that matches the hazard of the zone protection device onsite, the only zone protection onsite will be the backflow device you chose for the irrigation system.
Some things to consider when it comes to containment protection
1) Costs – You could get into big trouble financially if you miss the requirement for a containment protection device. Imagine the oval (zone) backflow device being 40mm and costing approx 2-3K for supply and installation and forgetting to price the containment protection. Imagine the school water meter was 100mm (extreme example) and you now had to install a 100mm backflow device to meet the requirement for containment protection. To supply and install a 100mm backflow device you could be out of pocket $5-10K.
2) Pressure losses – Backflow prevention devices are a point in the water supply where you lose a significant amount of pressure. By installing another device at the water meter, you may effect irrigation system performance
3) Vandal/thief proofing – Thieves love brass and copper. A backflow device could be an easy target
If you need any help with answering backflow related questions, please reach out to us.