Every piping system in a building follows the same three-part pattern: a source that supplies or receives the fluid, a distribution network that moves it, and terminals where it is used or collected. Supply systems (water, fire, gas, hydronic) are pressurized and flow outward from the source; drainage systems (sanitary, storm) flow by gravity from the terminals back to the source, which is the sewer.
Pressurized supply systems: domestic cold and hot water, fire sprinklers and standpipes, hydronic heating and cooling, irrigation, natural gas, medical gas, compressed air.
Air systems that protect drainage: vents, which let the drains breathe so traps keep their water seal.
Types of Piping Systems
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Domestic cold water (DCW)
Domestic cold water delivers potable water from the utility main to every fixture and piece of equipment, under pressure, without contamination.
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Source
Water service and tap at the utility main, with a curb stop or service valve at the property line.
Water meter (in a vault outside or a room just inside the building).
Backflow preventer (reduced-pressure zone or double-check assembly) protecting the public supply.
Pressure-reducing valve (PRV) when street pressure exceeds about 80 psi; booster pump package when it is too low for upper floors. Tall buildings split into pressure zones, often with a break tank.
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Distribution
Main across the lowest level or ceiling, feeding vertical risers, then horizontal branches on each floor.
Shutoff valves at each riser, branch and fixture; water hammer arrestors at quick-closing valves.
Pipe materials: copper (Type L/K), PEX, CPVC, stainless or ductile iron for large mains.
Insulation to prevent condensation (sweating) and freezing.
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Terminals
Fixtures: lavatories, sinks, water closets, urinals, showers, drinking fountains.
Equipment: water heaters (the start of the hot water system), ice machines, dishwashers, cooling tower make-up, hose bibbs.
Branch-level backflow devices at non-potable connections (boilers, irrigation, lab equipment).
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Domestic hot water (DHW)
Domestic hot water branches off the cold water system, heats it, and keeps hot water close to every fixture with a recirculation loop.
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Source
Water heaters: gas-fired or electric storage tanks, tankless (instantaneous) units, heat pump water heaters, or boiler-fed indirect tanks and heat exchangers.
Storage tanks, typically held at about 140°F to control Legionella.
Thermostatic mixing valve (master valve) tempering the supply to about 120°F for distribution.
Thermal expansion tank on the cold inlet, plus temperature and pressure (T&P) relief valves.
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Distribution
Hot water supply (HWS) main, risers and branches running alongside the cold water piping.
Hot water return (HWR), or recirculation, piping that loops back from the far ends of the system.
Recirculation pump with a timer or aquastat, and balancing valves on each return branch so every loop stays hot.
Insulated copper, PEX or CPVC; heat trace can replace a return loop on long runs.
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Terminals
The hot side of lavatories, sinks, showers, tubs and mop sinks.
Point-of-use mixing valves at public lavatories and showers to limit scalding (ASSE 1070 / 1016 devices).
Equipment: commercial dishwashers (often with a 180°F booster heater), laundry, kitchen equipment.
Cold water reaches fixtures directly and also feeds the water heater; the return loop keeps hot water moving so it arrives hot at the farthest fixture.
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Sanitary drainage (soil and waste)
Sanitary drainage carries used water and waste from fixtures down to the public sewer by gravity. Because it flows the opposite way from supply, its "terminals" are where waste enters and its "source" is the sewer connection.
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Terminals (where waste enters)
Fixtures, each with a trap (P-trap, or integral trap in a water closet) holding a water seal against sewer gas.
Floor drains and floor sinks, with trap primers to keep seldom-used traps wet.
Fixture arms (trap to vent connection) sloped at 1/4 inch per foot for small pipe.
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Distribution (collection)
Horizontal branches on each floor collecting fixture arms.
Soil stacks (carrying water closet waste) and waste stacks running vertically through the building.
Building drain at the lowest level, collecting all stacks; offsets and stack bases use long-sweep fittings.
Cleanouts at stack bases, changes of direction and set intervals along horizontal runs.
Pipe materials: cast iron (hub-and-spigot or no-hub), PVC or ABS; copper DWV in older work.
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Discharge point
Building sewer from where the building drain leaves the foundation (a few feet outside, per local code) to the public sewer main, or to a septic system.
Sewage ejector or sump pump for fixtures below the sewer elevation (basements).
Backwater valve where fixtures sit below the next upstream manhole rim.
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Vent and vent stack systems
Vents admit air to the drainage system so water flowing down the pipes cannot siphon or blow out trap seals, and they carry sewer gas safely above the roof. Vent piping carries air, not water, but it is built from the same DWV pipe.
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Source (connection to the drains)
Individual vent (revent) from each fixture arm, within the code's maximum trap-to-vent distance.
Common vent serving two fixtures back to back; circuit vent serving a battery of fixtures on one branch; wet vent where a drain pipe also serves as a vent for upstream fixtures.
Air admittance valve (AAV): a one-way mechanical vent, used where the code allows and a pipe to the roof is impractical (island sinks, remodels).
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Distribution
Branch vents collecting individual vents on a floor, rising at least 6 inches above the fixture flood rim before running level.
Vent stack: a dedicated vertical pipe paralleling the drainage stack, tied to it at the base and top.
Stack vent: the upward extension of a soil or waste stack above the highest fixture.
Relief and yoke vents that relieve pressure in tall stacks, typically every 10 branch intervals down from the top floor.
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Terminal
Vent through roof (VTR): extends above the roof (often 6 to 12 inches, more where snow or roof decks occur) and sits away from air intakes, windows and doors.
Waste falls down the soil stack to the building drain and sewer, while the vent stack and individual vents supply air from the roof so no trap is siphoned dry.
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Storm drainage
Storm drainage removes rainwater from roofs and paved areas, kept separate from sanitary drainage in most modern codes.
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Terminals (where water enters)
Roof drains with dome strainers, sized to the local design rainfall rate; scuppers and gutters on sloped roofs.
Overflow (secondary) drains or scuppers, set about 2 inches above the primary drain and piped separately, often discharging where they are visible.
Area drains and trench drains at plazas, loading docks and ramps.
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Distribution
Horizontal roof leaders under the roof deck, then vertical conductors (rain leaders) down the building.
Building storm drain at the lowest level; insulated where cold rainwater could cause condensation inside.
Cast iron or PVC; no traps or vents needed except where tied to a combined sewer.
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Discharge point
Storm sewer, retention or detention tank, bioswale, or rainwater harvesting cistern.
Storm sump pumps for below-grade areas.
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Fire sprinkler and standpipe systems
Fire protection piping stays full of water (or air) at all times so that a sprinkler opening over a fire discharges water within seconds. It is designed to NFPA 13 (sprinklers), NFPA 14 (standpipes) and NFPA 20 (fire pumps).
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Source
Fire service line from the utility main, separate from the domestic service, often through a detector-check meter.
Backflow preventer (double-check or RPZ) and a post indicator valve (PIV) or OS&Y gate valve outside.
Fire pump (electric or diesel) with a jockey pump to hold pressure, where city pressure is not enough; storage tanks where supply is limited.
Fire department connection (FDC): an exterior inlet so the fire engine can pump into the system.
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Distribution
System riser with the main control valve, alarm check valve, waterflow switch, pressure gauges and main drain.
Floor control valve assembly on each floor in high-rises (tamper switch, flow switch, test and drain).
Cross mains feeding branch lines, arranged as tree, loop or grid; black steel (Schedule 10/40) or CPVC in light hazard areas.
Standpipes: risers in exit stairs with hose valves at each landing (Class I for firefighters, Class II/III with hose for occupants).
Inspector's test and auxiliary drains for testing and draining.
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Terminals
Sprinkler heads: pendant, upright, sidewall and concealed; each opens on its own when a glass bulb or fusible link reaches its rating (commonly 155°F to 165°F).
Hose valves and cabinets on standpipe systems.
System types
Type
Pipe holds
Used where
Wet pipe
Water
Most heated buildings; simplest and most common
Dry pipe
Compressed air, water held back by a dry-pipe valve
Unheated garages, attics, loading docks
Preaction
Air; water released only after a detector also trips
Data centers, museums, archives
Deluge
Open heads; water flows from all at once
Aircraft hangars, fuel and chemical areas
The city main or fire pump keeps the system pressurized, the fire department can boost it through the FDC, and the riser splits water to each floor's sprinklers and the stair standpipes.
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Hydronic systems (heating hot water, chilled water, condenser water)
Hydronic systems are closed loops that move heat with water (or glycol) between central plant equipment and terminal units, then return it to be reheated or recooled. Unlike domestic water, the same water circulates continuously and is chemically treated.
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Source (central plant)
Heating hot water (HHW): boilers (condensing or non-condensing), heat pumps, or heat exchangers from district steam. Supply is typically about 180°F for older non-condensing systems and 120°F to 140°F for condensing boilers and heat pumps.
Chilled water (CHW): electric chillers (air- or water-cooled) or absorption chillers, typically supplying about 42°F to 45°F.
Condenser water (CW): an open loop carrying heat from water-cooled chillers to a cooling tower on the roof.
Pumps (primary, secondary or variable primary), expansion tank, air separator, makeup water with backflow preventer, and a chemical feed pot or treatment system.
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Distribution
Supply and return mains and risers, in a two-pipe system (heating or cooling) or four-pipe system (both at once).
Control valves (two-way or three-way) at each coil, balancing valves, isolation valves, strainers and air vents at high points.
Black steel, copper or press-fit pipe; insulated (chilled water with a vapor barrier).
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Terminals
Air handling unit (AHU) coils, fan coil units, VAV reheat coils and unit heaters.
Radiators, baseboard fin-tube, radiant floor and chilled beam systems.
Process loads such as data-center cooling units.
Each loop pumps conditioned water out to the coils and returns it to the boiler or chiller; the chiller's heat leaves the building through the condenser water loop and cooling tower.
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Irrigation systems
Irrigation is a low-pressure, zoned water system for landscaping, isolated from potable water and switched on by a controller.
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Source
Point of connection (POC) on the domestic service, a dedicated irrigation meter, or a reclaimed (purple pipe) or rainwater supply.
Backflow preventer (RPZ, PVB or double-check) above grade, usually the code's strictest requirement here because fertilizer and soil contact the water.
Master valve and flow sensor that shut the system down on a break; booster pump where pressure is low.
Controller (timer or smart weather-based) with rain or soil-moisture sensors.
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Distribution
Mainline: pressurized pipe (PVC Schedule 40 or Class 200) from the POC to the valves.
Zone (remote control) valves in valve boxes, each switched by the controller.
Lateral lines: smaller pipe or polyethylene tubing that is pressurized only while its zone runs.
Quick-coupler valves for hose connections.
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Terminals
Spray heads and rotors (pop-up) for turf.
Drip emitters, bubblers and microsprays for shrubs, trees and planters.
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Other building piping systems
These systems appear in many commercial, institutional and industrial buildings and follow the same source, distribution and terminal pattern.
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Natural gas (and propane)
Source: utility service, gas meter and regulator, earthquake shutoff valve where required.
Distribution: black steel or CSST piping, sized for low (about 7 inches water column) or elevated pressure with regulators at equipment.
Terminals: boilers, water heaters, furnaces, rooftop units, kitchen ranges and generators, each with a shutoff valve and sediment trap.
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Medical gas and vacuum (hospitals, clinics; NFPA 99)
Source: oxygen bulk tank or manifold, medical air compressors, vacuum pumps, nitrous oxide and nitrogen manifolds.
Distribution: cleaned and capped Type K or L copper, brazed under nitrogen purge, with zone valve boxes and area alarm panels.
Terminals: wall or ceiling outlets (inlets for vacuum) at patient beds, operating rooms and labs.
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Compressed air
Source: air compressor, receiver tank, dryer and filters.
Distribution: looped mains with drops taken off the top of the pipe; drains at low points.
Terminals: quick-connect outlets, shop tools, pneumatic controls and lab air.
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Steam and condensate
Source: steam boiler or district steam with a pressure-reducing station.
Distribution: steam supply pitched with the flow; steam traps separate condensate, which returns by gravity or a condensate pump.
Grease waste: kitchen sinks and floor drains to a grease interceptor before the sanitary sewer.
Acid or chemical waste: lab sinks through polypropylene or borosilicate piping to a neutralization tank.
Oil and sand interceptors for garages and vehicle maintenance areas.
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Water reuse and equipment drains
Greywater (lavatories, showers) and reclaimed or rainwater treated and piped in purple pipe to toilets, urinals and irrigation.
Condensate drains from AHUs and fan coils, piped to indirect waste receptors such as floor sinks.
Pure water (RO/DI) loops in labs and hospitals, in PVDF or stainless piping.
System
Flow
Source
Distribution
Terminals
Typical pipe
Domestic cold water
Pressure
Service, meter, backflow, PRV or booster
Mains, risers, branches
Fixtures, equipment
Copper, PEX, CPVC
Domestic hot water
Pressure, recirculated
Water heater, storage, mixing valve
Supply and return loops, recirc pump
Fixtures, dishwashers
Copper, PEX, CPVC
Sanitary drainage
Gravity
Fixtures and traps (inlet); sewer (outlet)
Branches, stacks, building drain
Building sewer, ejector
Cast iron, PVC, ABS
Vents
Air
Fixture arms, AAVs
Branch vents, vent stacks
Vent through roof
Cast iron, PVC, ABS
Storm drainage
Gravity
Roof and area drains
Leaders, conductors, storm drain
Storm sewer, cistern
Cast iron, PVC
Fire sprinkler
Pressure, standing
Fire service, fire pump, FDC
Riser, cross mains, branch lines
Sprinkler heads, hose valves
Black steel, CPVC
Hydronic
Closed loop
Boilers, chillers, cooling tower
Supply and return mains, control valves
Coils, fan coils, radiators
Steel, copper
Irrigation
Pressure, zoned
POC, backflow, controller
Mainline, zone valves, laterals
Sprays, rotors, drip
PVC, polyethylene
Natural gas
Pressure
Meter, regulator
Black steel, CSST
Gas appliances
Steel, CSST
Medical gas
Pressure or vacuum
Tanks, compressors, pumps
Zone valves, alarms
Outlets and inlets
Cleaned copper
Modeling Piping Systems
In a building model, each piping network is drawn as a piping system whose classification controls its color, calculations, and which elements can connect to it. Model the source equipment first, then distribution, then terminals, and connect every element to keep the system continuous.
Sprinkler families need correct coverage and elevation; coordinate with ceilings
Hydronic
Hydronic Supply and Hydronic Return
Boilers, chillers, pumps, coils, control and balancing valves
Connect supply and return to each coil connector; model insulation
Irrigation, gas, medical gas, compressed air
Other, or custom types built on Other
Equipment, pipe, outlets
Create named system types (for example Natural Gas) with their own color and abbreviation
Verifying the Model
Before issuing a model, use the system browser and interference (clash) checks to confirm every element is connected, classified, and clear of structure and ductwork.
