Per code properly sizing the supply line is very similar to properly sizing the sewer line.

In the code we have a table, which lists all the different types of fixtures and it assigns a "Fixture Unit" (FU) value to each fixture.

We begin by making a list of all the fixtures in the structure and adding the individual FU values to determine the "Total Load"

Once we have the total load need to know the Total Developed Length (TDL) of pipe from the source to the furthest fixture. Careful here, TDL not only includes the physical length of the pipe, it also includes the additional length attributed to fitting insertion loss. In lieu of the actual fitting insertion loss the code allows us to use 1.20% of the total physical length.

Once we have the total load and total length we consult another table that will give us the correct supply line size.

If you will make a list of all the fixtures in your house and email it to me I will be glad to work it all up, then return you a copy via email and post the result here for all to see. When making your list do not forget to let me know how many outside hose bibs you have.

LazyPup@yahoo.com

The connection at the city line may only be 3/4" anyway. My neighbor just got her old galvanized line removed and wanted to go with a 1" line but the city shut-off allowed only 3/4".

Check that out before you go and do any expensive digging.

Andy Christensen, CWS-II

The tap is and will remain 3/4" as I can't afford to pay the city over $1000 to upgrade.

I'll email you lazypup

Upsizing the pipe main to house one size is a good idea to avoid losing any more than your given potential. (depending on distance)

In many municipalities, the basic monthly service charge for water (the fixed fee you pay every month, before water usage is added) is based on the size of the line coming into your house from the meter. The larger the line, the higher the fee.

Before increasing the size of the service, perhaps you should ask your service provider to check whether or not you're being provided with adequate minimum water pressure on the provider's side of the meter. The problem could be low pressure at their end, in which case, they should come up with a solution.

In almost every place where I've been connected to a municipal water main, I've needed to have a pressure regulator on my side of the meter to reduce incoming water pressure. This is true where I live now, and my house is a good bit further than 200' from the street.

Far too often people get one of those silly little pressure gages that have a female hose thread adapter and attach that to a hose bib or laundry faucet and blindly assume the pressure they see is the actual working pressure of their system but such is not the case. When you attach one of those gages to a faucet then open the faucet to take the reading the gage is blocking the outlet thus for all intents and purposes they are still recording the pressure in a closed system. The basic laws of physics state that the pressure will remain constant at all points in a closed system however, the moment that we open a faucet and allow water to flow the pressure throughout the system immediately drops to "Dynamic Head Pressure" or more commonly stated as "Working Pressure."

Dynamic head or Working head pressure is Static Head pressure minus "Friction Head Loss" and "Vertical Static Head Loss".

Water physically weighs 0.434lbs per vertical inch column therefore to compute vertical static head loss we must measure the actual vertical rise from the point where we measure the pressure to the point of demand. As an example; let us assume a two-story house where the water line enters the basement near the floor and the shower is on the second floor. Typically we would have an 8 rise to the ceiling plus 1Â for the floor joists and flooring material on the first floor, 8.5Â to the ceiling and another 1Â for floor joists and flooring material to the second floor and finally a 5.5Â rise to the showerhead for a total vertical rise of 24Â. The vertical static head loss from the main water shutoff valve to the showerhead would then be 0.434psi x 24Â = 10.4psi loss.

Now assume that we measure the pressure at the main water shutoff valve and we get 45psi. This means that the absolute maximum pressure at your showerhead would then be 45psi minus 10.4psi = 34.6psi. From this we would then need to subtract friction head loss to determine the actual pressure at your showerhead.

In the original post they stated that the pressure and volume is fine when only one faucet is opened but it decreases rapidly as two or more demands are opened. That is because "Friction Head Loss" increases dramatically as the velocity of flow increases. By example, let us continue to examine what happens if just the shower is used.

Let us assume that in addition to the 24Â vertical rise there is a 10Â horizontal offset from where the supply line enters the basement to where it rises up to the shower therefore the total length of the line inside the house from the water main to the shower is 24Â vertical plus 10Â horizontal for a total of 34Â. (Technically we would need to also add in the fitting insertion losses but for now we will disregard them).

The post states that they have a ¾" supply line that is 200 long. Let us assume the line to the shower to be a ½" line 34 long and the shower is rated for a flow rate of 2.5gpm.

We measured 45psi at the main water shutoff valve and as was previously stated the pressure is constant at all points in a closed system so it then stands that the pressure at the prime mover (municipal main) is also 45psi however when flow begins friction head loss also begins at the prime mover.

The post states that the existing supply line is ¾" and let us assume it is continuous roll PE-SDR pipe (black poly-which has one of the lowest friction loss factors). Consulting the PE-SDR friction loss table we find that at 2.5gpm the loss is 1.5psi/100ft and we have 200 so the loss is 3psi from the municipal main to the main water shutoff valve.

Assuming the ½ line to the bathroom is copper we then consult the type L copper pipe friction head loss table and find that for the 34 run from the main to the showerhead we have a net loss of 0.118psi/foot x 34 = 4.02psi so at 2.5gpm the total friction head loss is 3psi + 4.02psi = 7.02psi (round off to 7psi)

The static head pressure was 45psi and dynamic head pressure is static head pressure minus vertical static head loss + friction head loss so the actual pressure at the showerhead is 45psi  7psi  38psi. That is not bad pressure if we could be assured that no one would turn on any other fixture while we are taking our shower however the plumbing code requires that when we design a water supply system it must be capable of maintaining certain minimum pressure standards in a worst-case scenario where all the demands in the structure are open simultaneously.

Under the UPC we would use the FU (Fixture Unit) method as I described in my previous post whereas under the IRC we use a minimum gpm rate for each fixture. Both methods will ultimately arrive at the same solution so for simplicity let us use the IRC demand rates here.

Bob sent me an email stating that he has the following fixtures:
4 sink faucets
2 toilets
2 bathtubs
1 shower
3 hose bibs outside

When I examined the list I was a bit confused. With 2 toilets I am assuming he has two bathrooms and one of the sinks is obviously a kitchen sink so I am guessing that he has a master bath with both a tub & a shower and perhaps 2 lavatories but on the other hand one of the sinks could also be a laundry sink.

From IRC table 2903-1 we get the following minimum pressure and flow rates to each fixture.

BathtubÂÂÂÂÂÂÂÂ.4gpmÂÂ8psi
Shower (temp controlled)Â3gpmÂÂ..20psi
LavatoryÂÂÂÂÂÂÂ..2gpmÂÂ.8psi
Kitchen sinkÂÂÂÂÂÂ.2.5gpmÂ.8psi
Water Closet(tank type)..Â3gpmÂ....8psi
Laundry hookupÂÂÂÂ..4gpmÂÂ8psi
Hose bib #1ÂÂÂÂÂÂ.5gpmÂÂ8psi
Hose Bib#2ÂÂÂÂÂÂ.5gpmÂÂ.8psi
TOTAL LOADÂÂÂÂ28.5gpm
Although not mentioned, if he has a dishwasher that would add another 2.75gpm.

Now let us examine the Friction loss table once again.
With a flow rate of 28gpm the velocity of flow through his ¾" PE-SDR line is 16.82feet/sec or more than 4 times the maximum allowable 4ft/sec and at this rate the line will exhibit severe pipe wall and fitting erosion resulting in premature line failure and the friction loss is 59.41psi/100 of pipe. Given that his line is 200 long @ 28gpm the total friction head loss is 2x 59.41psi = 118.82psi thus the friction head loss is more than twice the supply pressure of 45psi and with all fixtures open at best he would barely get a trickle of water and no noticeable pressure.

Even increasing to a 1" line would still result in a 36.5psi friction head loss from the municipal main to the main water shutoff at the house.

On the other hand if the line from the main to the structure was increased to 2" the friction head loss through the supply line would be reduced to 1.36psi and the resultant pressure at the house main shutoff valve would be 45-1.36= 43.64psi which remains slightly above the code minimum supply pressure of 40psi.

There is approx. 75' of 3/4" type "K" copper water main service in the street from the water service tap at the street main to my curb valve from there it travels approx.
90'before entering my home and going into the water meter.

I have 1 kitchen faucet and dishwasher; 1 1st level bathroom with one vanity faucet,1-bath tub with shower and one toilet bowl. 2nd floor: one shower(No tub); one vanity faucet and one bowl. Basement one washer hookup. Outdoor: 4- hose connections. I have spoken to the water Co. about the fact I can't take a shower and flush a toilet bowl with out losing significant water pressure. They acknowledged the excessive amount off copper piping in the street(probably due to an error when the service was brought to the house in 1953, it loops around a dead end street curvature and the back to the curb valve. I asked them about friction losses on so long a run, there answer was it doesn't affect the pressure and or volume. (right). They said that I should change my service size to at least 1". It is not feasible due to proximity of the service(under a concrete driveway) and all of the plants and land scaping along the way up the driveway. I suggested that they should abandon the old 3/4" service in the street and run a 1"service and tap from the main to my curb valve before considering a larger main on my property or installing a booster pump.