What are the Basics of Plumbing Systems?

  • 14 September, 2022

Candidates studying for the ARE® exam are required to have a basic knowledge of plumbing systems in building design. Specifically, this topic is covered in the Project Planning and Design exam. In addition to understanding how plumbing systems work, candidates should also be familiar with how fixture counts are typically determined by code requirements, as well as how the selection and placement of plumbing fixtures should be considered in terms of accessibility requirements. This blog post will focus, however, on providing a general understanding of the plumbing systems employed in buildings as a whole.

What are the Basics of Plumbing Systems?

1. Understanding How Plumbing Systems Work

While plumbing engineers are typically engaged in architectural projects of any significant size or complexity beyond single-family residential projects, architects must understand how plumbing systems work since the design of these systems may impact the architectural work and vice versa. Plumbing systems for typical building projects include lines for water supply, wastewater, and stormwater. If gas systems are utilized, such as for heating or cooking purposes, the design of these systems also falls within the scope of the plumbing engineer's work. In all cases, the plumbing systems must be designed to comply with the requirements of the plumbing and building codes which are adapted by the jurisdiction where the project is located.

2. Water Supply

Water supply is typically provided by connection to a public utility line, unless it happens to be a small building with water supply provided by a well. The amount of water which is used by the building is measured by means of a water meter located between the municipal line and the building's water system. In order to prevent supply water from flowing in the reverse direction, from the building to the municipal line, backflow preventers are utilized. The water supplied to the building from the public utility line is typically provided under pressure. The water pressure supplied will need to be checked, however, to make sure it is sufficient for the building. If it is not, booster pumps may be required, which is certainly the case for tall buildings, where it is required to have sufficient pressure for fixtures at the top of the buildings. In this case, a system of multiple booster pumps may be required since there are also maximum allowable water pressures in addition to the minimum needed pressures for fixtures. A control system is utilized to ensure that pump speed and water flow are adequate for the line. Elevated water tanks are another solution, though this is less utilized now than in the past.

3. Hot Water Supply

Supply water lines are typically divided in a building so that hot water can be provided as needed after passing through a water heater. There are multiple energy source options for water heating, including gas, electric, or even solar. There are, additionally, different types of distribution methods, including traditional tanks (or storage heaters), tankless or instantaneous/on-demand water heaters, combination water heaters, and point-of-use water heaters. Each may have its own advantages and disadvantages in terms of energy usage, system efficiency, and time required for the heated water to be provided at point of use.

4. Pipe Sizing

The pipe sizes necessary for a water system will depend upon the estimated water demands for the building as well as the number and type of fixtures that will be served by the piping. There are a number of different materials which are used for pipes, the most common include cast iron, copper, brass, and plastic. Individual pipes are connected with fittings, the material of which must be compatible with the material of the pipes which they connect. Architects should also be familiar with the use of valves, which are used to control the flow of water within a piping system, as well as the need for pipe clean-outs for maintenance purposes.

5. Wastewater System

Once the supply water is utilized within a fixture, such as in a sink, toilet, shower, drinking fountain, or washing machine, it is collected into the building's wastewater, or sanitary, system. This system conveys the water, sometimes referred to as effluent, to the municipal sewer or sanitary line, and on towards its ultimate point of disposal, such as at a municipal treatment plant, where the water is treated prior to its release into the environment. Smaller buildings, such as single-family residential buildings, which are at a remove from a public line, sometimes utilize a septic tank, which releases the water such that it is absorbed into the ground after its discharge from the system.

6. Sanitary Line Pipes

The sizing of the sanitary line pipes will depend upon the number and type of fixtures which are being used in the building. A minimum pitch for the pipes is necessary to ensure an adequate flow is established for the sanitary system. The architect should also be familiar with the need to vent the sanitary pipes. This is accomplished just after the used water leaves the fixture, with vertical piping that will typically rise to roof level. This allows for gas to escape from the system, regulating system pressure. Between the fixture and the vent pipe, a trap is located to prevent odors from leaking back into the space.

7. Gray Water Utilization

It should be noted that there is also the possibility of utilizing gray water for other uses, such as for irrigation purposes. Gray water is used water from fixtures other than toilets, which is sometimes referred to as black water. The use of gray water is governed by the code provisions of the local jurisdiction.

8. Roof Drainage

Where flat roofs are being used on a project, roof drains are typically utilized to carry stormwater collected at the roof. Although they may be referred to as flat roofs, minimal slopes of 1/4 inch per foot should be used so that the stormwater can be directed into the roof drains without the risk of pending. Scuppers located at parapet or secondary emergency drains should be used as a backup method of draining water from the roof in the case of the primary drains becoming blocked or clogged. Water collected at the roof drains is carried within a system distinct from the sanitary line. This stormwater system is typically connected to the municipal stormwater system. On projects where sloped roofs are used, rainwater may be gathered at gutters which convey the water to downspouts that are then either connected to the municipal stormwater system or, if the building scale and codes allow, directly to the exterior ground.

9. Harvesting Rainwater

A feature on some projects which aim for the sustainable use of water resources is to harvest rainwater for use at the project site for water conservation purposes. Rainwater is collected into tanks or cisterns in which it is stored for later use. Uses for collected rainwater are typically limited to exterior applications such as irrigation purposes.

10. Accounting for Sprinkler Systems

It should be noted that water supplied to the building may be divided into two lines, one for potable water and one for utilization in fire sprinkler systems, when they are required for a building. As for the potable water system, it is necessary that the pressure of the water supply be checked for pressure and flow rate. There are a number of different types of sprinkler systems, the differences between which will not be discussed here, but they include wet pipe, dry pipe, deluge, and pre-action systems.


An architect should be familiar with the plumbing systems noted above both to understand the requirements for a particular building as well as to work effectively with plumbing engineers and ensure proper coordination of building systems. Effective architectural coordination with the plumbing engineer will allow for system efficiency as well as spatial compatibility with the architectural design and the requirements of other building systems.

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About the Author: Adam Castelli

Adam Castelli is a licensed architect and engineer currently practicing in the Pittsburgh area. He holds a master's degree in architecture from the University of Massachusetts Amherst and a bachelor's degree in civil engineering from Villanova University.

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