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, which seems to be i the norm.

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)

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

Thanks

I don't think you'll see an increase worth the effort digging up the entire supply line from the meter to the house over a run of 25-30 ft.

1. 8GPM = 3 bedrooms + 1 baths typical .... Is This Enough?
vs at street
18GPM = 6 bedrooms + 3 baths typical
2. GPM restrictions include 3/4" meter/tap @ normal rates, so any improvements here cost much more/month THEN the pipe size/flow/friction over distance, as you noted
3. So you are interpolating a pipe size increase to follow City suit, expecting 8GPM to result in 16GPM = 4 BR 3BA needs? ... and we both are negating 30ft friction as too short a run to calculate vs say a 300ft run ...
4. If you need more than this and not fearing maintenace issues with valves later, then - sans superior mechanical engineering opinions on hand, consider a 1.25" pipe doesn't cost much more than 1" ... witnessed some of this solution thinking on my projects before a problem arises
5. you would be best served to have a GPM goal based upon #BR #BA, 1 or 2 stories of "head" then use a calculator if an engineer doesn't volunteer sage advice

https://extension.psu.edu/water-system-planning-estimating-water-needs

Yeah. Flow rate is related to the square of the diameter of the pipe, so that kind of loss seems about right. You'd see better flow rates if you change to 1". You may also consider going to PEX because you can do it all in one continuous run. It's also more flexible and a little less susceptible to leaks.

I don't understand the GPM drop from one side of the meter to the other. I would not expect any noticeable drop in pressure or flow from 1" to .75" over a short run like that. If they have 18GPM on their side, I would expect relatively close to that on yours. I have never worked with city water/pressures/regulators/etc so maybe something at the meter accounts for this.

I've only experienced changing from 1" to 1.25 and 1.5 over 50 feet and if there was a difference, It would require testing equipment to see it.

No matter what I would think the flow you have is plenty. If it were me, I would use it like it is for a bit and see if it suits your needs. Personally, I'm not digging up 30' of pipe unless there is a damn good reason for it, and mine are buried 2-10" from the surface, yours are probably all code compliant and stuff which means a lot more digging.