Split water line after backflow preventer and meter. 1

[jdeaneng]

I have a client that is putting in a new restaurant. There is a main water line coming into the site. He only wants to use one meter and backflow preventer. The line is splitting to go for potable water to the restaurant and also the irrigation, down the line from the backflow preventer. Is there any problem with this situation, for example, possible cross contamination?

 

[sam74]

I'm not sure about cross contamination but depending on your anticipated irrigation needs you might have an inflated sewer charge. I think most utilities/municipalities that provide both water and sewer services base your sewer fees base upon water usage. Therefore your irrigation usage would likely reflect on your sewer bill if your usage was not metered separately. That may or may not be your situation. You can google it and learn more.

From past experiences you typically don't split a water line beyond the meter until it is inside the building and out of your hands. Although I have seen cases where this has been proposed by some non-USA engineers. I am sure standard practices likely vary from country to country, state to state, and so on.

 

[LittleInch]

Depends on the elevation and profile of the irrigation line. If it is uphill from the tee then yes there is a theoretical back flow issue and contamination. If downhill or flat then there should never be sufficient head to flow back down the irrigation line whilst there is sufficient pressure to flow to the potable water connection.

Also depends on the guaranteed minimum pressure from the main after the meter to see if this is always higher than the max back pressure from the irrigation line, but I wouldn't like to rely on that as you would get contamination if the main valve were shut off or restricted in flow.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[cvg]

irrigation lines should always have a backflow preventer, regardless of elevation or how it splits off the main line. it is very commonly done around here but usually splits right at the building

 

[bimr]

There is no problem with a single meter and a backflow preventer on only the irrigation line.

You should install a second meter on the irrigation line so the client saves the water cost. Most places bill for the wastewater based on the potable water usage.

 

[77JQX]

Note to bimr: Our jurisdiction would also require backflow on the service to the restaurant.

 

[cvengr]

IMHO, the problem focuses on the irrigation system.

While some irrigation systems might be NonPotable water source systems, they aren't required to be NP. Check local codes.

Even if they are potable water, it isn't uncommon for irrigation systems to be designed by Architects...Interior Designers,..Decorators,...Landscape Architects,..yeah,..that's the one,..Landscape Architects, who typically cost estimate an order of magnitude above the market, while Civils tend to cost estimate within 10% of market values.

When Landscape Architects design your hydraulics, don't be surprised if they only rely on codes to insure backflow doesn;t occur in their systems,....i.e. antisyphoning devices in the irrigation components of their system.

Systemically, as a Civil Engineer, we protect ourselves by designing in the RPBFP, to insure NP water or tainted Potable water might not leak back into potable water systems. If the owner doesn't want to pay, let him face the permitting requirements which ensue, and distance yourself from your employer's decision.

Remember, this is still in the design phase. Many problems can still arise in construction. If the parties that be, have already taken this position, you need to pay special attention to requirements for special inspections, and insure you are writing into your notes adequate inspections so the construction is installed per code.

Also, you may have to notify the authority having jurisdiction, in addition to the owner, to comply with state law.

 

[bimr]

As noted by 77JQX, many areas require a backflow preventer for restaurants. So you will need two (1) backflow preventers, one for the restaurant and one for the irrigation line.

 

[John2025]

Agree with bimr et al. One thing to remember is the pressure drop across the RPZ valves. If you have low pressure to start, it may be a problem. Still need them, though.

 

[TGLG]

Typically, municipal standards are concerned with preventing the public main from being contaminated by your water service. The standards that I am familiar with prohibit any branches in the service upstream of the backflow prevention device. Downstream, though, the standards get a bit vague and it's left up to the judgment of the design professional.

I would recommend splitting the line downstream the RPZ, then putting a second backflow prevention device (a DCV) on the irrigation branch to protect the domestic line from an contaminants in the irrigation system. Just make sure that there is sufficient pressure available to overcome the pressure drop across two devices in series.