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How to Replace Your House Water Supply Pipe

Often a small water supply pipe size between the water company's big water main in the street and your house results in a low flow to the house. This can add a lot of cost to your new sprinkler system, as a lower flow means you will need more valve circuits. This FAQ explains how much benefit to expect from changing to a larger size house water supply pipe, and how to install the new pipe if you decide it would be beneficial. This FAQ is a sub-page to the City Slicker Water webpage, which is part of the tutorial on how to design a sprinkler system. While written in relationship to irrigation systems, the information here applies to any situation where you want to achieve a greater water flow to the house. It also should be helpful if you just need or want to replace the water supply pipe for the house.

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Before you begin any digging call 811. This is a FREE service available everywhere in the USA. "Every digging job requires a call even small projects like planting trees or shrubs. If you hit an underground utility line while digging, you can harm yourself or those around you, disrupt service to an entire neighborhood and potentially be responsible for fines and repair costs." See the 811 website for more details. They will come out and mark the locations of all the underground utilities for you. In addition to helping you avoid accidentally digging up a utility pipe or wire, this will also help you locate exactly where your existing water supply pipe is located! Again, both the phone call and the service are free.

tipBefore rushing out to replace the existing water supply pipe with a larger pipe, I suggest that you dig up some of the existing supply pipe and see what size it actually is underground. Often a larger pipe size (probably plastic) is used for the underground portion of the pipe, with a smaller size metal pipe at the end where the pipe comes out of the ground or extends into the basement. If all but 5 feet or so of the supply pipe is a larger pipe size, you probably don't need to replace it. In this case the larger pipe size you found underground can be used for the "New Replacement Pipe Size" when calculating a new Maximum Available GPM using the table below.

Potential New Maximum Available GPM Values
If you don't have a water meter, use the shut-off valve size
or smallest existing supply pipe size (whichever is smaller) in place
of the water meter size.
Water Meter Size New Replacement Pipe Size Maximum Available GPM when a new supply pipe is installed
Using new SCH 40 PVC supply pipe Using new PE (SDR-7) supply pipe* Using new Type L copper supply pipe Using new PEX supply pipe
5/8" 1" 15 GPM 15 GPM 15 GPM 15 GPM
3/4" 1" 17 GPM 17 GPM 17 GPM 17 GPM
3/4" 1 1/4" 20 GPM 20 GPM 20 GPM -
1" 1 1/4" 33 GPM 32 GPM 27 GPM -

New pipe sizes larger than those shown in the table above do not result in a higher Maximum Available GPM value. However, they may help you by reducing the pressure loss, which can also be beneficial. The Sprinkler Design Tutorial will explain this.

* PE pipe is not recommended. PE has a low burst pressure, and generally PEX pipe is now used in situations where PE was formerly used.

"Maximum Available GPM" is a value used in the Sprinkler System Design Tutorial at It is a measure of the maximum SAFE flow that the house water supply pipe can accommodate. It is possible to force more water through the pipe, however doing so may cause major damage to both the pipe and house's plumbing system over time. See the tutorial on Water Hammer and Air in Pipes for more information on pipe damage.

The table above is only for use in situations where the water is supplied to multiple households by a water supplier, such as a municipal water system. It is not suitable for use when water is supplied from on-site wells, streams, ponds, etc. For calculating how much water is available using an on-site pump (like with a well) see the Country Bumpkin webpage, for gravity flow sources see the Backwoods Water webpage.

Not all types of pipe listed are legal to use in all locations. Local building authorities regulate through building codes what type of pipe may be used. Codes change and it may no longer be legal to replace the pipe with the same type that was previously used. Local specialized plumbing stores may be able to help you with code compliance, however it has been my experience that advice on codes from larger regional and national outlets is often not correct. I recommend that you contact your local building authorities for advice on what type of pipe to use, often this requires just a simple phone call to them. Many will also offer very valuable tips and suggestions, be sure to also ask how deep the pipe must be buried.

How to replace your water supply line:

In most places a plumbing permit is required to replace the water supply pipe or even to simply cut into it. Contact your local building authorities for details.

Remember that the water supply pipe carries the water you and your family drink! It is important to be careful not to get dirt into it when working. After completion of your work be sure to turn on all your water faucets for several minutes to flush out any dirt or other contaminates. You should sterilize the pipes before using the water from them for drinking. There are products available at plumbing stores for this. Be sure to buy the pipe sterilizer and read the instructions before you start work as you may need to put the sterilizer into the pipes before you reconnect them!

Water mains, Goosenecks, and Corporations Stops

The water company has a large pipe someplace out there that is called the "water main". It is probably 6 inches or larger in diameter and located in the street or alley. From the water main a smaller pipe goes to your property. This smaller pipe is referred to as a "gooseneck". At the end of the gooseneck is a shutoff valve called a "corporation stop". The corporation stop is typically installed near your property line. The idea is that the corporation stop marks the dividing point between you and the water supplier. The pipe coming into the corporation stop belongs to the water supplier. The pipe going out of it typically belongs to the property owner. The corporation stop is usually located in a box or at the bottom of a sleeve with a round plastic or metal cap on it. The cap may only be 4" in diameter and hard to find. Often it will be covered with dirt or grass, so you will need to poke around to find it, try probing the ground with a pitchfork, metal rake, or screwdriver. Look for a mark engraved into the curb or street pavement indicating the location. The corporation stop will probably be buried below the frost line, so it may be several feet deep in colder areas.

tipCall 811 and they will come out and mark the location of the water gooseneck for you, and it's free! This is very helpful in finding the corporation stop since it is someplace on the gooseneck. That will narrow your search area. Sometimes they will even mark the location of the corporation stop. The person who comes out to mark the pipe locations generally has detailed plans that show the exact location of everything. If you happen to be there and are friendly, they are often willing to share lots of useful information with you.

The corporation stop (often abbreviated as "corp stop") serves as the water company shut-off valve for your house. It is usually operated using a special key or wrench in order to prevent unauthorized use. Fortunately, you can buy a wrench for it at most hardware stores. Get out a flashlight and look at top of the corporation stop first to see what shape the operating nut is, as there are several styles. Also note how deep it is so you can get a wrench with a long enough handle to reach it. Most use a slotted wrench that fits over a raised rectangular shaped bar, like the one in the photo below. If you're really lucky, it will have a normal handle on it, but don't bet on it! In some cases you have enough room to operate the corporation stop using a standard pipe wrench. Another trick is to use a basin wrench (a special wrench used to install faucets on sinks) to operate it. You will probably also notice a couple of holes on the corporation stop that align with each other when the valve is in the closed position. These allow the water company to padlock it closed if you don't pay your water bill! Most corporation stops are hard to turn, so you may need to put some muscle into it. You may be able to get the water company to send someone out to close and open it for you. Often they will do this for free (especially if you ask nice, and you have a good record of paying your water bill on time!)

Corporation Stop Valve, Water Meter, Shut-Off Valve
Photo of an underground water service utility box
containing a corporation stop, water meter, & homeowner shut-off valve.

The photo above is of a particularly nice set-up. Not only is there a corporation stop but there is also a homeowner shut-off valve with an easy to use handle. No need to use a special key, the homeowner can turn off the water themselves without tools in an emergency. I cleaned up the inside of this box before taking the photo. A valve box like this will often have ants, spiders and other disgusting stuff in it so be careful when opening them up. I even found a dead turtle in one once!

Sometimes in cold weather areas there is not a corporation stop located outside. The corporation stop is in your house, usually in the basement, crawl space, or a utility room. In this case you're pretty much screwed, because the water service pipe is likely owned by the water company and even if it isn't you can't easily shut off the water to replace it. Before giving up, call your water company directly (use their local customer service number, not 811) and ask if they have a shut-off someplace between their mainline and your house. Maybe you just couldn't find it. As a last resort, ask them if they will install a new, larger supply pipe for you. Most of the time they will, but they probably will charge you for doing it. Don't be surprised if they refer you to a plumbing company to actually do the work.

Add a Second Pipe or Replace the Original Pipe?

How you proceed from here depends on the current layout of your water supply, your budget, and future maintenance concerns. Select the method below that best applies to your needs.

The water meter is installed right next to the corporation stop, or you don't have a water meter.

The water meter is installed more than five feet away from the corporation stop (typically inside the house.)

The options for pipe replacement are essentially the same as those above, however in this case you need to replace the pipe between the corporation stop and the meter. Typically in this situation the meter is inside the house. However, if the meter is someplace out in the yard you will also need to replace the pipe between the meter and the house.

It is much easier if you don't actually replace the short section of pipe that goes into the house through the wall or floor. Reconnect the new pipe to the old, smaller pipe about a foot outside of the house wall. That leaves a short section of the old pipe going into the house, but is a lot easier than replacing the pipe through the wall or floor. The water will squeeze through the short section and it will work fine as long as there isn't more than 5 feet of old pipe left between the point you connected the new pipe and the water meter. If there is more than 5' left, you will need to install new pipe through the wall, or replace the old pipe inside the house once it is through the wall. In other words you leave a short section of the old pipe going into the house through the wall. Once inside it is easier to install a new, larger pipe. You will tap in your new sprinkler system as close as possible after the water meter. Unfortunately, you will have to route the new sprinkler supply pipe out through the wall, which means you will have to drill a hole in the wall. Be sure to seal the hole around the pipe with a good quality flexible water-proof caulking compound! The pipe will move as it expands and contracts, so the caulk needs to remain flexible after it has cured. (Do not use cement for sealing the hole! Standard cement, plaster, and concrete mixes are NOT waterproof!)

Other Items to Consider

Plastic pipe must generally be installed at least 18 inches deep, measured from the top of the pipe to the soil level. All pipe should be installed below the frost line. In some areas that might be 4 feet or more deep. Your local building authorities will have specific requirements on how deep the pipe must be.

tipHow do you connect the new pipe to the old? Most professionals use a compression coupling. If you don't know what that is, ask at a hardware store. If you make a threaded connection between plastic and metal pipe see the How to Connect Plastic Pipe to Metal Pipe FAQ.

Well, that's it for this FAQ. Have fun, and remember, safety first when digging and working with trenches. Follow all OSHA requirements. See OSHA's guide to working around trenches.