# How can I determine what size main water meter is required?

The main water pipe into our house is only a 1" ID pipe, but the city decided to install a 2" water meter for us, which has a significantly higher monthly service charge than a 1" meter (over \$1000 more per year).

I found a couple of websites (like this one) that calculate the required water-meter-size based on the number of showers, toilets, sinks, and such in the house. They all place us solidly into the 1" size range. But we live on a hill and the incoming water pressure into our house is only 35psi. So I'm trying to understand the following things:

• Do I need to correct the required water meter size for the lower pressure? If so, by how much?
• If the main pipe to the house is only 1" ID, would a water meter bigger than 1" even help at all?
• Is a 1" water meter equivalent in "size" (as far as flow impedance goes) to a 1" water pipe?

One of our neighbors with an identical floorplan said he got the city to swap his meter out for a 1.5" at no charge and is not noticing any difference other than the \$600 annual savings. I'm trying to figure out if it makes sense to be even more "aggressive" and have them down-size us to a 1" meter.

Note: This question is purely about things to consider when determining the right size of our water meter. I'm not looking for any off-topic policy advice on how to deal with the city.

• I take it you have a big house that requires a 1" pipe? In my experience, most residences need a 3/4" main. Feb 14, 2014 at 6:07
• @Edwin 1" was pretty standard around my area, even for smaller houses. Feb 14, 2014 at 6:23
• @Edwin We have about 3100 sq-ft. 3 full bathrooms, pool, sprinklers. We end up somewhere around 45 to 65 "fixture units" worth of water needed (depending on which site I use to calculate it, main difference are the sprinklers). 1" water meters seem to be the ones intended for anything between 38 and 89 fixture units. Feb 14, 2014 at 16:35

It's likely that the type of meter you have is called a PD meter.

PD Meters are very accurate, but do this at the expense of pressure.

My guess is that increasing the volume of the meter likely does do a little to reduce pressure drop. However, without the actual specs for each meter, it's impossible to say how much.

That said, **it is highly unlikely that a 2" meter in the middle of a 1" line it's making a \$1000 (or even \$400) per year difference in pressue. For less than \$1000 you can can make a one time investment in a residential pressure booster.

• what do you mean that it is highly unlikely that it's making a \$1000 per year difference? Where I live, in Philadelphia, the annual service charge difference between a 2" meter and a 1" meter is \$690.48 (excluding storm-water fees). Doesn't seem unreasonable that the OP's district would be 50% more. Do you mean that the benefit of the larger meter doesn't equal \$1000? Feb 14, 2014 at 6:04
• I like the idea of a pressure booster, could go down to a 3/4" with one. Feb 14, 2014 at 6:09
• @Edwin I mean the reduction in (to borrow an EE term) 'resistance' in a 1" meter vs 2" meter (especially given it's in the middle of a 1" line) is not going to come anywhere close to providing \$1000 worth of value. If he needed the full capacity of a 2" pipe and had one comeing in off the main, then it would be worth it. Feb 14, 2014 at 6:10
• @Edwin,virtualxtc I love the idea of the pressure booster and considering to go down to even 3/4". That would save me another \$200 a year! But this does raise some additional questions, that I decided to put in a separate question here: diy.stackexchange.com/questions/39027/… :) Thanks! Feb 14, 2014 at 7:08

I (literally) dug up the information on our water meter: Currently we have a 2" Neptune T-10 installed. On their website they offer specifications for their different meters, including charts of pressure drop vs. flow-rate. I used some free software to quickly digitize the plots and stick them together onto one chart showing the pressure drop vs. flow rate for 4 different meter sizes:

So, if I assume (please correct me on these assumptions if they make no sense) that a 10% pressure drop would be noticeable (for us: 3.5psi), then I would hit this drop at 18gpm for a 3/4" meter and at 33gpm for a 1" meter. Given that the shower valve we installed provides 8gpm at 75psi (so probably less at 35psi), that means 2-3 people can take a shower at the same time with a 3/4" meter and more than 4 for a 1" meter.

So, I guess going with a 3/4" meter feels a little tight to me (unless we get a booster pump, of course), but a 1" meter should probably be just fine. I don't think we'd frequently be using more than 15gpm anyway, which would only imply a pressure drop of 1psi over the 2" meter.

Note: I'll leave @virtualxtc's answer as the selected one, since he pointed me in the right direction and summarizes things nicely.

• Do a test of how much water your shower uses. Shower heads reduce the flow a lot. In the US, federal law limits shower heads to 2.5 gpm at 80 psi since 1992. But, maybe you have older ones or modified them? Feb 14, 2014 at 19:11