Depending on your location, your city water may come from various sources, such as a nearby lake, river, or underground aquifer. Water is collected, sent to a water treatment facility, stored in a tank or water tower, and then transported through underground pipes throughout the city, eventually reaching your home. The water is delivered under pressure, usually between 40 to 80 psi.

If you’re not on city water, you likely get your water from a well. However, there are some areas where it makes sense to use a water storage tank or cistern, or the water comes from a nearby stream or spring. For this explanation of how things work, we’re going to stick to wells as the non-city water source. 

A well is a way to access an aquifer - porous, underground rock that holds water. The depth of your well depends on the local geology and how far down an adequate water supply is found. It can range from 25 to over 500 feet. This depth can vary greatly within a small distance, sometimes just a mile or so. Additionally, some areas have minimum well-depth requirements. 

A pump brings the underground water up to piping that transports the well water to your house. The water is typically not treated like city water is. Soil and rocks act as a natural filter, although chemicals can still leach into aquifers, especially if it’s a shallow aquifer. 

The top of the well should be easily located, but sometimes, you have to snoop around to find it. If you can't locate the wellhead visually, look for faux rocks or an odd-placed bush. If it's an older well, the wellhead might be in a pump house (a separate structure built to house the well equipment), buried underground, or you might have a well pit. A well pit will likely have a concrete cover. Well pits are not allowed anymore, and a buried well head is inconvenient and likely unsanitary. In both cases, it's recommended to raise the well casing and install a pitless adapter.

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When a faucet is turned on, water readily flows out at a rate that makes it easy to use for stuff like washing dishes or taking a shower. For that to happen, the water needs to be pressurized. City water is pressurized from the source. Well water is pressurized with the help of a pressure tank, gauge, and switch. There are also constant pressure systems available for wells. 

Within the house, piping carries water to all the fixtures that use water. Once the water has left the fixture and enters a drain, the drain/waste/vent (DWV) plumbing system takes over.

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If you’re on city water, water enters underground from the street through a 3/4” or 1” pipe. This is called the “service line.” The pipe should be buried at least six inches below the frost line, but it depends on local restrictions. However, it should be deep enough to prevent damage, especially if the pipe runs under a driveway or walkway. 

The pipe material could be metal (e.g., copper, galvanized steel, cast iron, or lead) or plastic (e.g., PVC, CPVC). In houses built before the 1960s, the pipe is usually galvanized steel; after the 1960s, it’s likely copper.

If you have lead service lines, federal programs are helping communities identify and replace them. Lead can leach from lead pipes and enter drinking water, which is dangerous because it is a potent neurotoxin for both children and adults. If you have a lead service line, contact your water provider to check on options for testing the water and replacing the pipe. In the meantime, it’s recommended that you flush pipes with cold water for several minutes before using water for drinking or cooking, and to use a water purification system with a certified lead-reducing filter.

Note: You might see a wire attached to your metal service line. This is likely a ground or bonding wire. If you have a plastic service line and you happen to dig up your water line in your yard, and you find a wire on that plastic pipe, that wire is a tracer wire, allowing the utility company to locate the buried water pipe.

A residential well is typically 6 inches in diameter. Lining the well is a casing pipe that protects the water supply from rock bits, soil, other debris, and underground critters. But the water actually travels through the drop pipe that’s inserted in the well casing. From the drop pipe, the water goes through a pitless adapter (near the top of the well but below the frost line) that connects the drop pipe to the pipe that takes the water to the house. The pipe that carries the water into the house is usually plastic, either PVC or polyethylene. 

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Well Pump

Unless the aquifer is an artesian well (an artesian well is an aquifer that has enough positive pressure to bring the water to the surface), a pump is needed to get the water up out of the well. There are two main types of pumps: a jet pump and a submersible pump. 

A jet pump pulls water up by creating suction with an impeller. It comes in two varieties, a single-pipe pump for shallow wells (about 20 to 25 feet deep), and a two-pipe (sometimes called a convertible jet pump) pump for wells up to about 100 feet deep. With either type, the pump housing sits at the top of the well, not in the water. However, with a deep jet pump, part of the pump (the ejector and Venturi valve) sits down in the well. This is why a deep jet pump needs two pipes. 

Jet pumps are easier to work on, because they sit above the water, but they use more energy and aren’t considered as reliable as submersible pumps.

A submersible pump is a cylinder that sits down in the well near the bottom. It’s more energy efficient than a jet pump and more effective in deeper wells. The pump uses pressure to raise the water through the drop pipe. Submersible pumps are more expensive than jet pumps, but are considered more reliable. 

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If you pay for water and sewage, you’ll have a water meter. If you share a well, you might have one. The water meter is usually located near where the water line enters your house. The meter is usually inside along that pipe, but it could be on the pipe just before it comes into your house. Or, it could be located in a pit (called a “curb box”) between the house and the street.

Your water usage is measured and recorded as the water passes through a water meter. Your water provider will take readings to know what to charge you for usage. Some meters can be read remotely. However, some municipalities still read them manually. You might have a city worker stop by, or they might contract with a company to come by and take a reading. Or, some cities allow self-reporting. 

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Water utilities distribute water by pressurizing it, either by using gravity (a water tower) or pump stations. The pressure moves the water through municipal pipes and into your home. If your city uses a water tower, the tank at the top of the tower sits higher than the homes around it so that gravity can create pressure and distribute the water. 

In most cases, the water pressure is determined by the difference in elevation between a city water tank and your home. The greater the height difference, the stronger the pressure. Water pressure can vary from neighborhood to neighborhood if there’s a difference in elevation. It can also vary within a house. Since pressure drops as it rises (it has to fight against the force of gravity), water pressure will drop 5-10 psi for each floor it rises through a house.

If your city doesn’t use a water tower, pump stations are used to create pressure. This can create more uniform pressures throughout an area, but there still might be some difference depending on the distance from the pump station. 

With city water, it usually enters a house between 40 to 80 psi (pressure is measured in pounds per square inch, abbreviated psi). If the pressure is higher than 80, most areas require a pressure regulator or pressure reducing valve. This will likely be installed just after the main water shut-off valve. If it’s lower than 40, you might want to install a booster pump.

While many people like strong water pressure, water pressure that's too high or too low can cause problems. The ideal water pressure for a home is between 60 and 70 pounds per square inch (psi). Too high (over 80 psi) water pressure can damage pipes, fixtures, and appliances. Too low (below 40 psi) can make it difficult to shower, wash dishes, or run multiple appliances at once.

A hose-bib gauge provides an accurate way to track water pressure. The gauge is inexpensive and available at most hardware stores. When attached to an outdoor spigot (use one that’s closest to the incoming water line), the gauge reads the pressure level, which should fall within the range of 40–80 psi.

Note that water pressure is different than water flow. Water pressure is the force of water measured in pounds per square inch (psi), while water flow is the volume of water flowing through your system measured in gallons per minute (gpm). Pressure and flow are related but different, and the flow coming out of a fixture isn’t necessarily an indication of your water pressure. You could have high pressure in the pipes, but low flow if there’s a clog or you have low-flow fixtures.

Water pressure for a well system is created with the well pump and a pressure tank (the pressure tank can be inside or outside the house).* It’s regulated with a pressure gauge and switch. The pump pulls water up through the drop pipe, into the water line, and to the pressure tank. (Technically, a jet pump pulls water up, and a submersible pump raises water with the use of pressure.) 

The pressure tank can vary in size from 30 to 80 gallons. Inside the tank, the water is separated from the air in the tank by a rubber bladder. The air is pressurized to settings determined by your system and set when the tank was installed. There’s a switch on the system with a cut-in (reset point) and cut-out (trip point) setting. The switch sends a signal to the well pump to turn on when the pressure in the pressure tank drops to the cut-in point. As water fills the tank, the pressure rises. When it reaches the cut-out point, the switch sends a signal to the pump to shut off. Typical cut-in and cut-out pressures are 30 psi and 60 psi.

Older pressure tanks don’t have a rubber bladder. They still pressurize the water with air, but there’s no physical barrier. 

*If you don’t have a pressure tank, you have a submersible pump. A submersible pump raises water out of a well using pressure and doesn’t need a pressure tank to provide water to a house, but a pressure tank is highly recommended in order to ease the strain on the pump.

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On the water line entering the house, you’ll find a water shut-off valve. When you have a water meter, you might have a shut-off valve before and after the meter. The valve allows you to shut off the water supply to the entire house. You should mark this valve with something very visible (like a brightly colored tag or piece of ribbon) so that if a pipe or fixture springs a leak, anyone can quickly identify the correct valve.

The valve could be a round knob type (called a gate valve) or a lever-looking valve (called a ball valve). Gate valves are older and prone to damage, and they can become stuck due to corrosion. Ball valves are preferred for main water shut-off valves. 

Note: You should test your shut-off valves once a year to ensure they will turn off in an emergency. However, never force a plumbing valve if it’s hard to turn.  If you have a valve that feels stuck, try applying a penetrating oil and let it sit for a while. Then, gently try to work it back and forth until unstuck. 

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Within your house, some plumbing pipes may be exposed if you have an unfinished basement or crawl space, but the majority of your plumbing pipes are behind walls. 

Once the water enters your house, in the traditional system, pipes called “trunk lines” carry water to areas of the house that use water, including your water heater. These pipes are typically 3/4” in diameter. However, pipes going to outside faucets or other fixtures with high water demands could be 3/4” in diameter. Just like a tree with a trunk and branches, pipes that carry water from trunk lines to one or two fixtures are called “branch lines.” Generally, these are 1/2” in diameter, or 3/8” for toilets.

The water supply pipes could be metal or plastic. Metal varieties include copper, galvanized steel, brass, and a braided stainless steel flexible tube (the stainless steel encases a rubber tube; this is often seen under sinks or behind toilets). Plastic varieties include CPVC (chlorinated PVC - regular PVC is not used for water supply), PEX (easily identified by red and blue plastic pipes but can also be white), polybutylene (PB), and a flexible reinforced type of PVC tube (usually seen on fixtures where the pipe will be visible).

There isn’t a perfect water supply pipe, and each has its own issues, often depending on the quality of the product, installation, and water quality. 

Copper can develop pinhole leaks and pitting from acidic water. If the water is too soft, copper can leach into the drinking water. 

Galvanized steel can corrode over time, but does so from the inside out, so you can’t always see the corrosion. The zinc coating is worn off by flowing water, this exposes the steel which then rusts. The zinc coating on older galvanized steel (up to the 1960s) might contain lead. As the coating wears off, lead is deposited in the drinking water. 

Brass can corrode similar to galvanized steel, but it depends on the water quality, and usually takes a long time. .

CPVC can become brittle and crack, especially when exposed to cold temperatures. 

PEX is the latest (and greatest?) type, but it’s not without some issues. Leaks can occur from improper installation, poor quality brass fittings, physical damage from kinking or rodents chewing, or pinholes from highly chlorinated water, especially hot water. 

Polybutylene (PB), or “poly B," was used from 1978 to 1995. It looks similar to PEX, with the same type of fittings, but is gray. It can be easily identified by markings on the pipe that say “PB 2110.” It was an inexpensive alternative to copper. However, over time, the molecular bonds in the material decay and come apart, causing pinholes, cracks, and catastrophic leaks. Exposure to chlorine, high water temperatures, and high pressure all cause PB piping to deteriorate. Because the product was new and quickly became widely used, installation errors were also a problem. Some insurance companies will not insure homes with PB piping. Most plumbers will recommend replacing PB piping as a preventative measure.

The method of connecting pipe sections depends on the type of material the pipe is made from. Even then, there can be different ways to connect a particular material. In general, copper pipes are soldered together, brass and galvanized steel use threaded fittings, PVC is joined using glue or threaded fittings, and PEX uses crimp or compression fittings. (Note: Fittings are used to connect pipes together, often combining pipes coming from different directions. Common ones include elbows, tees, wyes, and crosses. Fittings might also include a valve to regulate flow, a cleanout to provide access, or to help join pipes of different diameters.)

You can have more than one type of pipe material in your house. The different types of pipes can be connected or run separately to specific fixtures. Two things to note when connecting dissimilar pipe materials: 1) Nearly all areas prohibit gluing dissimilar plastic pipes; special fittings should be used. 2) Certain metals cannot be joined directly. For instance, copper cannot be joined to galvanized steel, as this will cause galvanic corrosion (one metal will corrode faster because the water acts as a conductor, carrying ions from one metal to another). To connect the two, a dielectric union (a specialized type of fitting) is used. 

As mentioned, PVC is typically bonded using glue. A primer is usually applied first, followed by a special adhesive that chemically melts the plastic, resulting in a chemical weld. If you're considering a DIY plumbing project, remember that different adhesives are required for various types of plastic pipes; you cannot use an adhesive designed for one type on another. Always read the labels to ensure you’re using the appropriate product. While some adhesives are rated for multiple types, some local codes may have restrictions.

Ensure pipe sections are connected correctly using approved methods for your area. If not, you may end up with a leak. Even if it doesn’t leak, a home inspector will likely flag the incorrect connection when you sell your home.

With PEX or polybutylene piping, you may have a different type of distribution system called a “homerun” that uses a manifold. In a homerun system, hot and cold water are piped to a main manifold distribution device. The manifold has a connection spot for every plumbing fixture in the house. There, PEX piping is connected to that connection spot and travels straight to the fixture. The PEX piping only serves that one fixture. It uses a lot of PEX piping, but there are no fittings (connections) in the walls. 

Or, you may have a “submanifold” system. With this, the PEX is piped similar to a traditional system with trunk lines, but each room that uses water has its own small manifold. 

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Every fixture should have a shutoff valve on both the hot and cold pipes. This is so that repairing the single fixture doesn’t require shutting off the entire house supply at the meter valve. Fixture shut-off valves are usually angle stop valves, but you might see a gate or ball valve. 

If you have a homerun manifold system, shutoff valves for each fixture will be at the manifold. These should be clearly marked. However, some homerun systems have both a manifold shutoff and a shutoff at the fixture.

Note: You should test your shut-off valves once a year to ensure they will turn off in an emergency. However, never force a plumbing valve if it’s hard to turn.  If you have a valve that feels stuck, try applying a penetrating oil and let it sit for a while. Then, gently try to work it back and forth until unstuck.

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You might have a valve on a shower or faucet that prevents wild temperature changes when another fixture is turned on. This can help prevent scalding and is a good idea if there are children or elderly in the house.

There are two primary types of devices to do this: pressure balance valves and thermostatic valves. The main difference between the two? A pressure balance valve senses and controls the ratio of hot and cold water. It’s usually built into a one-handled faucet (the lever controls both hot and cold) or could be installed near the water heater. 

A thermostatic valve senses and controls the actual water temperature. It has two knobs, one for temperature and one for flow. There are lots of different faucet handle designs for a thermostatic valve, but if you have one knob that sets the temperature and the other adjusts the flow, you likely have a thermostatic valve. (These are different than two-knob faucets, where there is a separate knob for hot water and another for cold water.)

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If you have an area of the house that is a fair distance from your water heater, you might have a hot water circulating pump. This is installed on piping that forms a loop between the fixture and your water heater, keeping hot water in that loop so that when the fixture is turned on, hot water doesn’t need to travel the distance from the water heater to the fixture. 

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Backflow is when non-potable water (water you don’t want to drink or cook with) flows backward into the potable water supply. How can that happen? Remember that pressure differences drive the movement of fluid materials. If the pressure of the water supply drops (for instance, when a city water main breaks, or a fire truck pumps water from a nearby fire hydrant), the drop in pressure can make the water from your house flow backwards into the city system because the water pressure is now higher in your house. 

Normally, with plumbing fixtures, there is a physical space between the sink and the faucet. So if you have a sink filled with dirty, soapy water and a water main breaks, the air space between the water in the sink and the bottom of the faucet will prevent backflow. But what if you have a hose attached to an outdoor faucet and it happens to be in a bucket of yuck. That yuck will get siphoned into the city water supply. (FYI, this is called a cross connection.) When this happens, it’s a huge expense for the city. 

Backflow doesn’t happen often, but it has happened enough that some codes now require backflow preventers. Local codes vary, but many require the valve for spots where there’s no physical air space, or the air space could be bypassed with a hose. The most common spot for a required backflow preventer is on an automatic irrigation system for landscaping. Other potential problem spots include outdoor faucets, any laundry sink with a threaded faucet to attach a garden hose, and certain boilers. Most toilets made since the 1970s have backflow prevention included. Some municipal water providers are now installing backflow preventers just after the water meter. 

Often, when a backflow preventer is required, annual testing by a licensed backflow tester is also a requirement.

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Water Hammer Arrestor

Water hammer is a term used to describe the loud banging or knocking that can occur in pipes. It’s caused by a sudden change in direction of the water flow or when the water suddenly stops. This abrupt change generates a pressure surge, and the resulting shockwaves in the pipes produce the noise you hear. While the noise can be a nuisance, the larger issue is the stress that the pressure surge places on your pipes, fittings, and joints. (FYI, the larger the pipe diameter, the greater the pressure force. In large municipal water pipes, closing a valve suddenly can significantly damage the pipe.)

Because the pressure surge is caused by a sudden change in direction or stop, turning a faucet off slowly can prevent it from happening. But appliances like a clothes washer or water softener have an automatic valve that doesn’t close slowly. To prevent water hammer, there are water hammer arrestors that can be installed on the pipe. This provides a “safety offramp” for the increased pressure.