Plumbing in the Home/Low pressure or volume


Hi Dana,
We purchased this house a year ago and I had the water company come out and check my home because I had recently bought a new lawn sprinkler and had to take it back because I got very little coverage with it, it goes up only about 6 feet with nothing else going in my house.
The water company guy said that I need a plumber to check it out and I wanted get your opinion as to what the problem may be.
House built in 1947 and I'm not on a hill. The supply line coming into the house is 3/4 inch, piping in basement is all copper and no pressure regulator.
Water company changed the meter last year and it seemed to make a difference, but still having problems watering lawn.
I checked the water pressure and it is showing 56 psi. Piping in the house is 1/2 inch off the 3/4.
My next door neighbor has the same type sprinkler and he is getting much better coverage with it 20' at least and his home was built in 1925.
With the sprinkler running my 1.6 gal toilet takes 6 minutes to fill, without sprinkler running it fills in a minute.
Water company suggested that it may be the coupling from the water main to my water supply is 5/8 going into 3/4 line, if this were the problem I would think this is pretty expensive to replace as main is on my side of street, but still would need to open street up. I plan to talk to city to see if they may have any info on this as I don't want to explore into ground if I don't have to.
Also, when water company changed meter they turned on water and said that something seemed to be restricting flow there (in basement coming into house). Could changing the water shutoff fix the problem?

Hopefully I have given you enough details.
I have looked at installing a booster, but this would be about $1500 to $2000.
Is this something that can be somewhat easily diagnosed? Any other ideas, or is there other things I can do to help diagnose?

Thanks for your help.

Hello Bill,
Pressure and flow rate, although somewhat related, are two different things. Have you checked the pressure at the house end of the system just for a baseline?

The determining factors for flow rate are;
1. Size of piping
2. Condition of piping
3. Number of elbows in the run.

All three above contribute to what is called "fiction loss" and high friction loss will result in a much lower flow rate.

The sizing of plumbing systems is typically done by calculating "fixture units of demand". Each fixture unit is equivalent to about 7.5 gallons per minute.
A water piping system is sized by calculating the total demand in fixture units as well is the demand on each branch that serves a fixture that comes off the main supply line.

The water company may have given us a clue here. I have seen 5/8 (nominally called 1/2 inch inside diameter) copper used on a mainline on older homes. A 5/8 copper line in good condition with few bends (elbows) in it is technically capable of delivering only 4 fixture units of flow, depending on the length. A 7/8 (3/4 inch interior diameter) under the same conditions will deliver 12 fixture units of flow.

Since your mainline is typically buried, determining its size can be difficult and may require some excavation. It could be three-quarter inch all the way from the meter to the house but if the meter is only a 1/2 inch (5/8) then that would be a severe restriction on its ability to deliver the needed demand. The total available flow rate is determined by the greatest restriction in the line. The weakest link theory applies here.

The first steps in diagnosing this issue is to get an actual pressure measurement where the water enters the house. Then, somehow, you need to try to determine the effective flow rate in gallons per minute. Doing this can be tricky since drawing water off from a fixture somewhere typically introduces a restriction because of the design of the valve supplying the fixture. This may require the services of a professional.

These are only baseline measurements.  If they are less than desirable, which I assume they are, you have to now attempt to diagnose the cause. That may involve some digging,and checking with the water company about the actual size of the meter they installed.

Installing a booster system is generally done for low pressure reasons, not to improve flow rate. The actual flow rate is determined by the delivery system as explained above. A pressure booster pump can only work with what it has available and increase its pressure. It cannot realistically increase the flow rate. It should be noted that the standard rating for any fixture connected to a water system is only rated to handle a maximum of 80 PSI.

Out here in California, all of the water meters are typically set in a vault very near the curb on the property side, not in the street. I have replaced literally hundreds of mainlines and rarely, if ever had to actually go into the street. Here, that requires a special license that most plumbers don't have and significant expense obviously since you typically have to repair any sidewalks as well as the street itself.

(A mainline sewer line is a whole different ballgame. Sometimes you do have to go into the street to replace them. Typically, at least here, the city stubs a sewer line inside the property line for you to connect to. The property owner is typically not responsible for the portion that lies within the city street but that varies with a jurisdiction. Here, the property line is determined by a measurement from the center of the street.)

Good Luck,

Plumbing in the Home

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Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


Retired, Licensed General Contractor with Plumbing license. Active Home Inspector, Litigation Consultant and Infrared Thermographer, Online Marketing specialist.

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