Domestic water system

A domestic water system is a system within a building, generally a house or a business, that provides water, provides ways to use water, and provides means of removing waste water. The system usually comprises several components:

Cold water supply

Most modern western water systems are directly fed from a municipal water system by a high-pressure pipe, usually located under the street. Many houses still use a cistern or a well where a convenient water system supply is not available; they usually use a pump and pressure tank to maintain system pressure. Older houses (or houses that need gravity fed cold water, i.e. for a power shower) may also have a cold water tank. In such a case, drinking water (usually the kitchen tap) is usually fed directly from the main water supply due to the risk of contamination in the cold water tank.

The supply may or may not be metered. Non-metered supplies are usually billed based on the size of the house (making assumptions about the number of people living in the house). However, such accommodations are increasingly rare.

Internal distribution system

Within a building, the water is distributed through a series of pipes to the point of use, which is generally either a tap, a fixture, or an appliance. A tap is simply a water outlet without an accompanying fixture. A fixture is a device that uses water without an additional source of power, such as a toilet / WC (water closet) / lavatory, kitchen sink, washbasin, shower, or bath/bathtub. An appliance is a device that uses water coupled with an additional source of power, such as a washing machine, dishwasher, or icemaker.

Piping materials

At one time, lead pipes were used for water supply distribution. Then the standard became galvanized steel piping, then copper piping. Today, many systems use either CPVC (chlorinated polyvinyl chloride) or polyethylene piping, but many plumbers refuse to use these in favor of copper. Copper is regarded as superior due to its durability, rigidity, repairability, and ability to double as a whole-house ground. Plastic pipes are much easier for homeowners to install and repair without the assistance of a plumber.

Water heating

Domestic hot water is provided by means of water heaters, appliances intended to provide a hot water supply within the structure as well as a cold water supply.

Internal DWV system

DWV stands for drain, waste, vent, and these are all distinct features of an internal wastewater system. Drain refers to the acceptance of nominally clean water runoff, as from precipitation, while waste refers to sanitary waste water from fixtures and appliances. The vent is a system provided to eliminate positive and negative pressure within the wastewater system.

Traps

Each fixture, appliance and drain in a wastewater system must have a trap (also known as a water trap or an S-bend). This is a dip in the pipe that remains permanently full of water, preventing sewer gases from freely invading interior space. In cases such as floor drains that are not used as drains for long periods of time, water with a small amount of bleach should be poured into the drain periodically to maintain a sanitary trap seal.

Single-Loop systems

Old installations used a "single-loop" system, wherein a single vent was installed at the top of the entire plumbing stack. This meant that every fixture and appliance had to drain directly into a central plumbing stack that was usually (in the United States) four inches in internal diameter, with a minimum of three inches, so that the stack could act simultaneously to drain and vent.

Double-Loop systems

Today, most localities require a "double-loop" system, wherein each individual fixture and appliance must have its own dedicated vent, coming off the drain just beyond the trap, and rising at least six inches above "flood-rim level" before joining with any other vent (flood-rim level is the level at which the fixture or appliance can overflow if the drain is stopped and the water is kept running). Most or all vents are then joined into a common vent that rises through the roof. Most locales require that the vent through the roof be at least three inches in internal diameter.

Other requirements

Other requirements for a wastewater system include a cleanout where the drain leaves the house. This is simply a threaded plug that may be removed for convenient cleaning of the drain, using a snake or auger.

Piping materials

Older wastewater systems use cast-iron pipes for all pipes three inches and above, and often for two-inch pipes. Smaller pipes (1 1/2 inch and 2 inch) were generally lead at first, then copper. The cast-iron pipes, termed "soil pipe", was usually joined by inserting the straight (spigot) end of one into the flared (hub) end of the other. Oakum was then packed into the hub around the spigot, and molten lead was poured in to complete the seal. Most joints of smaller pipes into the drain pipes would involve brass ferrules, over which the smaller pipe would be pressed, then molten lead wiped around the joint to effect a seal (a "lead-wipe" joint).

Today, most wastewater plumbing systems use schedule 40 PVC (polyvinyl chloride). This is jointed using fittings that the pipe fits into with a close tolerance, the joint being sealed with a glue after a solvent cleaner (or primer) is used. Drain systems that do not carry wastewater can often use the lighter schedule 20 or 30, while many heavier commercial applications may require the heavier schedule 80. The cast-iron soil pipe is often still used, but it is used without the hub system, "no-hub bands" being used to join the straight ends of two pieces. These are rubber collars that overlap both ends, and sealed in place with overlying metal bands tightened with hose clamp type devices. Cast-iron pipe is "fire-safe" unlike PVC, and is also a lot quieter then PVC or ABS. Because of this, cast-iron is commonly used in industrial dwv systems. PVC is virtually the only pipe used in newer residential applications today, and ABS is mainly used for repairing old systems that used ABS.

Sewage

In areas where centralized sewage-handling systems are available, sewage is usually provided coupled with water service. The sewage is transported under low pressure, most often only under gravity flow, to sewage treatment plants before being flushed back into natural water systems (either river or sea).

Septic systems

In rural locations where a sewer connection is impracticable, sewage is often processed with the help of septic tanks and fields. These usually include lateral lines that allow the wastewater to seep into the soil throughout the septic field. Extreme caution is needed to prevent ground water from being contaminated by sewerage.