# Measuring functional flow.

I was wondering how you measure the functional flow rate of a homes supply.
When I took my class back in 2011, the instructor taught us to use a measuring cup. To time how long it took to fill X number of cups in X number of minutes. I don’t remeber his formula and I have miss placed my note book.

16 cups per gallon, how many cups can you fill in 15 seconds x 4…4 in 15 seconds x 4 is 16 cups = 1 gallon per minute, thats if you plan to actually use a single cup to measure.

Or you could use a dual pressure gpm set up.

It is not a measurement, it is an observation as to functionality.

Functional Flow: A reasonable flow of water supply at the highest and farthest fixture from the building main when another fixture is operated simultaneously.

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If the residence is on a well a recorded gpm is available at the court house, or by listing agents. I like the formula you gets have posted, do you use this for city water mostly?

Listen to Larson,
Go to the furthest bath from the supply, turn on the sink and/or the shower and flush the commode. If you have enough water to wash with while the toilet tank is refilling your ok.

Being in Arlington TX, all TREC requires is to have 2 faucets on at the same time and then flush the toilet. If the flow drastically changes, write it up.

Did you by any chance do your training with AHIT? If yes, then the measuring cup thingy was to fill up a 2 cup measuring cup in 7 seconds (pretty much what Jamin said). The reason behind this was to know how many gallons of water went down the drain in X amount of time. Should something happen, you would be able to tell plumber an estimation of how much water was used.
Over time, you won’t be needing the measuring cup as you will be able to look at the flow and guestimate it.
This estimation can help you especially when the house is its own septic system.

What happens when you have a water economizer fixture and it works fine with low GPM?

14 sec. means a 50% savings, and it is “wrong”?

The water economizer fixture won’t make a difference for this application since you are only filling up one cup at 7 sec. or 2 cups at 14 sec, it will just mean that you open the faucet a little more to have a flow of 1 gal/min.
The idea is that you have all faucets running at 1 gal/min so that you can make a quick calculation of how much water went down the drain.

I use a simple idea no formula I just open the kitchen sink faucet connect my hose to the washing machine connection and let her rip when I get to the bathroom there needs to be enough volume to get a decent shower and have never had a problem with this

The other reason for turning all faucets on at the same time is to make sure they all drain properly. I’ve had a few times when everything drained fine when just a coupe faucets were on, but when all were on it backed up.

I wasn’t asking because I didn’t know, it does make a difference.
When you restrict flow, even at max pressure the GPM will change…

You can’t open the valve more than it is rated for. Your not going to fill the cup in the Home Inspector School Standard of time.

You are correct, i should have been more precise in my explanation. The typical water economizer has a flow rate of 1.5 gpm. That is sufficient for the home inspection school test. If you come to a house that has a lower rate then it’s not that big of a deal. The reality of this test is 1) making sure there is no huge drop in flow when you have multiple faucets on and you flush the toilet and 2) that all lavatories and sinks drain as intended.