Guess this falls in the realm of fluid dynamics.
Or just plain old experience.

Recently purchased home. Noticed the GPMs at the 1st point of entry into the home for the water was low, approximately 4 GPM. 55 PSI

Called the city to have them check it at their side of the meter: about the same. They volunteered they had an issue too.

The repaired the feed to the meter, which included replacing their 0.75" feed between the city line and their side of the meter, with 1". Now getting 18 GPM at their side of the meter.

On our side, between 25 and 30' of 0.75" line (starts as poly but changes over to PVC at some point) from the meter to the 1st point of entry.

Now we're getting ~8 GPM. The GPMs essentially doubled. Much better.

My question (finally): Is that 18 GPM decrease down to 8 GPM about what should be expected when reducing from 1" to 0.75"? Or about what should I be seeing (obviously more than 8 but less than 18) ?

If it's necessary to change the line to the house, now is the time for me to do it before we extend our driveway and cover the path the line would take.

Thanks all

(Side note: Shout out to the City of Tomball water district. Between the time I called them to have someone come check it out to the day the line was replaced was only 3 days (Mon to Wed). I thought their response was great)

all of your fractions disappeared

Need to know your pressure, but on average you should see around 12-14 gpm through a 3/4" pipe at residential pressures (40-60psi)

Odds are you have some buildup or possibly collapsing of the pipe from the meter to the house. Honestly, since it's only 30-ish feet, I'd replace it all with 1" sch 80 pvc with a single expansion loop at the midpoint.

redaszag99 said:

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all of your fractions disappeared

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Thanks



Hey MODS, can you edit the title? Change it to "Expected GPM Change when Pipe Reduced from 1" to 0.75"

schmellba99 said:

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Need to know your pressure, but on average you should see around 12-14 gpm through a 3/4" pipe at residential pressures (40-60psi)

Odds are you have some buildup or possibly collapsing of the pipe from the meter to the house. Honestly, since it's only 30-ish feet, I'd replace it all with 1" sch 80 pvc with a single expansion loop at the midpoint.

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Good point I forgot to add the PSI.

When I measured it (before the city came out)it was ~ 55PSI.

Pressure seemed adequate, just the flow was low (sounds like a late night commercial)

And yes, I've considered just placing new line, but the dig isn't gong to be real fund.

I have to go a new route, (to avoid going under the existing driveway, dodge a gas line, the 1st 10 or so feet will be be through a thicket of roots, then about 12' in a narrow gap between the edge of the existing drive and a fence,...). Doable, just kid of a pain.

And I'm wondering how much I'm gaining by upsizing to the 1", considering once the line enters the house it reduces back down to 0.75"?

Thanks for your post

schmellba99 said:

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Need to know your pressure, but on average you should see around 12-14 gpm through a 3/4" pipe at residential pressures (40-60psi)

Odds are you have some buildup or possibly collapsing of the pipe from the meter to the house. Honestly, since it's only 30-ish feet, I'd replace it all with 1" sch 80 pvc with a single expansion loop at the midpoint.

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That's pretty high flow in 3/4" of pipe.

~44ft of loss per 100-feet of pipe. For the OP example, that would be ~ 14psi of loss in sch80 ABS/PVC. He'd have only 40psig of water at the house which, IIRC, is low for residential (but maybe no, I just deal in the commercial world).

It's also possible the city meter has a flow regulator on it to limit the flow to his house.

Also, google says that 6-12 is 'normal' for most homes with 2-4 people.

OP, if your fixtures are all flowing OK, then you're probably fine. Adding 1" may increase the flow some, but is it worth the cost/time to do it if everything works?

Over 30' of .75" PVC, at 8 GPM, you should lose about 2.5 psi from one end of the pipe to the other.
Edit: assuming pipe is level. Subtract .43 psi for ever foot of elevation gain.
Edit 2: Converting to 1" pipe should net you an additional 2 psi at the house, at 8 gpm.
https://www.omnicalculator.com/physics/friction-loss

What about 150' and going down about 8' in elevation, coming out of a 1/2" house line? If I just stick with 1/2", will I get any flow down the hill? Would bumping up to 3/4 do anything? I don't think it would.

Trying to put water and electricity in the lot behind my house that I own to one day park a boat down there. I don't want to open up a new account with the city for the lot. Would rather just run water down there from the house. Would be nice to flush the motor and wash down the boat rather than do all that in the driveway and then go park the boat in the lot.

Milwaukees Best Light said:

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What about 150' and going down about 8' in elevation, coming out of a 1/2" house line? If I just stick with 1/2", will I get any flow down the hill? Would bumping up to 3/4 do anything? I don't think it would.

Trying to put water and electricity in the lot behind my house that I own to one day park a boat down there. I don't want to open up a new account with the city for the lot. Would rather just run water down there from the house. Would be nice to flush the motor and wash down the boat rather than do all that in the driveway and then go park the boat in the lot.

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8' of elevation drop is going to help you to the tune of 3.4 psi. If you want 5 gal/min of flow at the end of 150', you should probably go with 3/4" line. Over 150', at 5 GPM, you'll lose 5 psi. At same flow and distance in 1/2" line, you'll lose 36 psi.

A 3/4" at 18. gpm isn't going to work very well. I ran two cases for you. At 18 gpm and smooth (PVC etc) pipe, sch. 80.

The pressure drop through 1" is 13.9 psi per 100 ft equivalent length (EL). Velocity is 7.9 fps.

That flow through a 3/4" gives 50.6 psi per 100 ft EL., velocity is 13.1 fps.

EL is equivalent length which accounts for fittings, e.g. one short turn radius elbow is equivalent to 30 pipe diameters in length.

As someone has already said each ft. of elevation gain or loss is worth 0.43 psi.

If you want me to run more cases like this let me know.

TxAg20 said:

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Over 30' of .75" PVC, at 8 GPM, you should lose about 2.5 psi from one end of the pipe to the other.
Edit: assuming pipe is level. Subtract .43 psi for ever foot of elevation gain.
Edit 2: Converting to 1" pipe should net you an additional 2 psi at the house, at 8 gpm.
https://www.omnicalculator.com/physics/friction-loss

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TxAg20, I appreciate your reply.

McInnis, please feel free to join in on the replies.

Allow me to rephrase my question as I think it may have been misconstrued.

The water flow/GPM from the city main to the city is via an ~15' section of 1" poly line, yielding ~18GPM at the meter.

Water flow/GPM from the the meter to the 1st entry point at our house is via an ~30' section 0.75" PVC, yielding ~8 GPM/55 PSI at the entry point.

What I'm trying to determine, is that drop from 18 GPM to 8 GPM within the norm of what I should expect when reducing the pipe from 1" to 0.75", over an ~30' section of 0.75" pipe?
Or, is there something restricting the flow beyond what's expected?
Flow/GPM is my main point of interest at this point as I think my pressure (55 PSI) is good.

Hope that's clearer and more to the point.

And thanks to all for the input and discussion

RC_57 said:

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TxAg20 said:

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Over 30' of .75" PVC, at 8 GPM, you should lose about 2.5 psi from one end of the pipe to the other.
Edit: assuming pipe is level. Subtract .43 psi for ever foot of elevation gain.
Edit 2: Converting to 1" pipe should net you an additional 2 psi at the house, at 8 gpm.
https://www.omnicalculator.com/physics/friction-loss

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TxAg20, I appreciate your reply.

McInnis, please feel free to join in on the replies.

Allow me to rephrase my question as I think it may have been misconstrued.

The water flow/GPM from the city main to the city is via an ~15' section of 1" poly line, yielding ~18GPM at the meter.

Water flow/GPM from the the meter to the 1st entry point at our house is via an ~30' section 0.75" PVC, yielding ~8 GPM/55 PSI at the entry point.

What I'm trying to determine, is that drop from 18 GPM to 8 GPM within the norm of what I should expect when reducing the pipe from 1" to 0.75", over an ~30' section of 0.75" pipe?
Or, is there something restricting the flow beyond what's expected?
Flow/GPM is my main point of interest at this point as I think my pressure (55 PSI) is good.

Hope that's clearer and more to the point.

And thanks to all for the input and discussion

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Best I can calculate, you should expect to drop from 18 gpm to 11.5 gpm over a 30' section of 3/4" PVC assuming straight and level pipe. Any restrictions, turns, or increase in elevation will have a negative effect on flow.

8 GPM is about where you should be. The 1" coming in to the meter is more or less irrelevant. You have 55psi through a 3/4" line. That is right at 8gpm flow rate.

TxAg20 said:

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RC_57 said:

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TxAg20 said:

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Over 30' of .75" PVC, at 8 GPM, you should lose about 2.5 psi from one end of the pipe to the other.
Edit: assuming pipe is level. Subtract .43 psi for ever foot of elevation gain.
Edit 2: Converting to 1" pipe should net you an additional 2 psi at the house, at 8 gpm.
https://www.omnicalculator.com/physics/friction-loss

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TxAg20, I appreciate your reply.

McInnis, please feel free to join in on the replies.

Allow me to rephrase my question as I think it may have been misconstrued.

The water flow/GPM from the city main to the city is via an ~15' section of 1" poly line, yielding ~18GPM at the meter.

Water flow/GPM from the the meter to the 1st entry point at our house is via an ~30' section 0.75" PVC, yielding ~8 GPM/55 PSI at the entry point.

What I'm trying to determine, is that drop from 18 GPM to 8 GPM within the norm of what I should expect when reducing the pipe from 1" to 0.75", over an ~30' section of 0.75" pipe?
Or, is there something restricting the flow beyond what's expected?
Flow/GPM is my main point of interest at this point as I think my pressure (55 PSI) is good.

Hope that's clearer and more to the point.

And thanks to all for the input and discussion

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Best I can calculate, you should expect to drop from 18 gpm to 11.5 gpm over a 30' section of 3/4" PVC assuming straight and level pipe. Any restrictions, turns, or increase in elevation will have a negative effect on flow.

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Ok, so I'm about 3.5 GPM short of expected.

The path from the meter to where it turns to the vertical to get in the house (~30' vertical rise to the hose bib) is fairly level.

And as far as turns, I'm only aware of one 45 (within a foot of where it leaves the meter) and then two 90s (a horizontal 90 just to turn towards the vertical rise into the house, and the last 90 to transition the run from horizontal to vertical).

Also, the line leaving the meter towards the house is poly. The last section (~6') as it turns to and up into the house is PVC-40. Somewhere along the other ~24' of line is a connection between the poly and the PVC, but it's under the driveway.

Would or could the above (the turns, the connecting point from poly to PVC) account for the 3.5 GPM drop?

schmellba99 said:

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8 GPM is about where you should be. The 1" coming in to the meter is more or less irrelevant. You have 55psi through a 3/4" line. That is right at 8gpm flow rate.

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That puts me at ease a bit.

schmellba, what are you doing to calculate/determine what you said above?

Way back when I purchased our first house I installed a sprinkler system and my GPM sucked. Called the city water folks and they tested the flow and brought in a larger line but left the old meter. So I gained some GPM but not what was on the upstream side of the meter.
Called them again and they said the meter was old and to small for what they had changed and needed changed to allow more GPM. The meter itself will cause a loss anyway.
They installed a larger meter and I then had plenty of GPM.
That's all I got.

Are you using a hose bib on your house off the 90 to get the GPM?

RC_57 said:

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schmellba99 said:

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8 GPM is about where you should be. The 1" coming in to the meter is more or less irrelevant. You have 55psi through a 3/4" line. That is right at 8gpm flow rate.

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That puts me at ease a bit.

schmellba, what are you doing to calculate/determine what you said above?

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I used an online calculator, nothing special.

Any idea what material the .75 line going to the house is? An old galvanized steel pipe is going to give you a lot more friction loss than pvc or poly

Oops. Saw you said poly then pvc. My bad.

I'm going to say it's a newer model meter as it's remotely read, has a screen on it that goes through different modes, etc.

smstavinoha88 said:

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Are you using a hose bib on your house off the 90 to get the GPM?

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Yes, as right at the pint where he line goes from vertical to horizontal and enters the house.

My GPM reading is based off the old time how long it takes to fill a 5 gallon bucket. Repeat the process 2 or 3 times to look for consistent times.

Most hose bibs are necked down inside and that could definitely affect flow rates. If there is a hose bib vacuum breaker on the hose bib, that could affect it as well.

Yes sir. But if the meter still has 3/4 inlet and outlet? And not sized up to the 1" they just added… would that not restrict the flow? I know it did in my case. Can somebody comment on that?

Gunny456 said:

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Yes sir. But if the meter still has 3/4 inlet and outlet? And not sized up to the 1" they just added… would that not restrict the flow? I know it did in my case. Can somebody comment on that?

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Almost every single inline flow measurement I've ever installed has been a smaller diameter than the parent line. The smaller diameter helps to eliminate any cavitation, air, etc. in the line so you get a full pipe of flow that can be accurately measured. Restriction through the flow orifice is pretty minimal and doesn't have any meaningful impact.

So why did they tell me I needed the larger meter due to the more GPM required by the sprinkler system? I know it made the world of difference for me.

The max operating GPM for a 3/4" meter is 35GPM, while the max operating GPM for a 1" meter is around 55GPM. I tried to attached a chart to show the difference, but the 3/4" meter starts reducing pressure around 3GPM, while the 1" meter starts reducing pressure around 10GPM. With the irrigation running and any other usage, you were probably getting close to the max accurate flow for the 3/4" meter, so it was in the best interest of the city to upsize to a 1" meter to ensure they are accurately measuring all usage, especially high usage when irrigation is running.

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Thanks. Great info and answers the question. Much obliged!

I use steel pipes for this calc.