Terminology

• Gravity delivery: pressure from the height of the storage above the outlet
• Booster pump / pressure set: pump that supplies pressure when gravity is not enough
• Pressure-reducing valve: limits static pressure in the system
• Make-up water: potable or reclaimed supply that refills the tank at a low level
• Air gap: open space that separates the make-up supply from the water level
• Nonpotable outlet: hose bibb, faucet, or open pipe carrying nonpotable water
• Dual plumbing: separate potable and nonpotable piping in a building

Standards

• Pressure by height: the greater the vertical difference between storage and outlet, the greater the pressure
• Pressure by use: showering needs much more pressure than drip irrigation
• Pumps: needed only where the system is pressurized
• Code provisions: pump access, pressure limits, make-up water, backflow protection, pipe identification, signage, and testing are in the plumbing code reference
• Backflow: make-up connections and any connections to potable systems use backflow protection

Components

• Pump set: submersible or surface pump with pressure tank or variable speed control
• Controls: float switches or level sensors that stop the pump at low level and call make-up water
• Make-up valve and line: with an air gap and a full-open shutoff on the make-up line
• Filters: upstream of the pump and at the point of use
• Pressure-reducing valve: where pump pressure exceeds the allowed static pressure
• Distribution piping: identified and separate from potable piping
• Signage: at each nonpotable outlet
• Locked outdoor outlets: hose connections in a locked vault or requiring a removable key

Detailing

• Separation: keep distribution piping apart from potable piping and building sewers as the code requires
• Access: removable access for pumps, valves, and filters
• Protect the pump: water must not fall below the pump intake; automatic make-up valves hold a minimum level
• Place the pump room: near the tank, drained, and heated or insulated where freezing occurs
• Identify piping: labels or color per code at regular intervals and at every outlet
• Test: pressure test the make-up and distribution piping before use
• Document: provide an O&M manual with schematic, parts list, and maintenance schedule

Uses

Specific uses

• Toilet and urinal flushing
• Irrigation systems
• Cold water laundry
• Vehicle and equipment washing

Pros and cons

Pros

• Gravity delivery from an elevated tank needs no pump
• A packaged pump set is a standard plumbing product
• Make-up water keeps flushing running through dry periods

Cons

• Pumps need power and maintenance
• Dual piping and signage add cost and coordination
• Make-up supply needs backflow protection and an air gap

Manufacturing and cost

Construction

• Packaged pump sets with controls and a pressure tank or variable speed drive, installed with filters and a make-up valve

Main manufacturers and suppliers

• Xylem
• Franklin Electric
• Pentair
• Watts

Trade association: ARCSA, American Rainwater Catchment Systems Association.

Sources

• Grafman, L.: To Catch the Rain, section 2.7 end use, https://eng.libretexts.org/Bookshelves/Environmental_Engineering_(Sustainability_and_Conservation)/Book%3A_To_Catch_the_Rain_(Grafman)/02%3A_Components/2.07%3A_End_Use
• Wikipedia: rainwater harvesting, https://en.wikipedia.org/wiki/Rainwater_harvesting
• UpCodes: 2024 IPC Chapter 13 nonpotable water systems, https://up.codes/viewer/general-services-administration/ipc-2024/chapter/13/nonpotable-water-systems