10.2 Nonpotable Rainwater Catchment Systems (UPC Chapter 16 as Amended by Washington)
Key Takeaways
Washington's 1602.1 requires AHJ approval of rainwater catchment systems supplying water closets, urinals, trap primers, irrigation, water features, and cooling towers, except exterior irrigation piping.
A rainwater system may have no direct connection to potable or reclaimed water; makeup water must enter through an air gap or reduced pressure principle backflow preventer (UPC 1602.4).
A permit is not required for an exterior rainwater system used for outdoor drip and subsurface irrigation with a maximum storage capacity of 360 gallons (UPC 1601.3).
Rainwater supplied to water closets, urinals, trap primers, and drip irrigation must pass a filter of 100 microns or finer (UPC 1602.9.11).
Pumps supplying water closets, urinals, and trap primers must deliver at least 15 psi residual at the most remote outlet (UPC 1602.9.6).
What Chapter 16 Covers
A nonpotable rainwater catchment system collects rain from roofs or other manmade aboveground surfaces, stores it, and supplies nonpotable uses. L&I lists Chapter 16 in the Part 1 content. Potable rainwater systems are in UPC Appendix K, which Washington does not adopt.
Washington 1602.1: Installation, construction, alteration, and repair of rainwater catchment systems that supply water closets, urinals, trap primers for floor drains and floor sinks, irrigation, industrial processes, water features, cooling tower makeup, and other uses must be approved by the AHJ. Exception: exterior irrigation piping.
Permits, Design, and Maintenance (UPC 1601)
| Section | Requirement |
|---|---|
| 1601.3 Permit | A permit is required. Exception: exterior systems for outdoor drip and subsurface irrigation storing no more than 360 gallons |
| 1601.2 Design | By a person registered or licensed for plumbing design, or who demonstrates competency. The design professional requirement is waived for irrigation systems of 360 gallons or less. Components must be listed |
| 1601.5 Maintenance | Inspection per Table 1601.5; the owner keeps the maintenance log and is responsible for maintenance |
| 1601.9 | No mercury-containing controls in contact with rainwater |
| 1601.10 Separation | Underground rainwater piping is separated from the building sewer per 609.2. It may share a trench with potable water at 12 inches vertical and horizontal separation where both materials are approved for use in buildings |
| 1601.11 Abandonment (WA 1601.11.1) | Disconnect, drain, plug, and cap. Washington adds that abandoned components may not be reused for potable water. Underground tanks are drained and filled or removed |
| 1601.12 Sizing | Rainwater distribution piping is sized per Chapter 6 |
Connections and Makeup Water (UPC 1602.4)
- No direct connection to a potable supply or an alternate water source system.
- Potable or reclaimed makeup water is allowed only through an air gap or a reduced pressure principle backflow preventer.
- Both systems must have the valves and air or vacuum relief needed for deactivation and draining during a cross-connection test (1602.9.2). An initial test is required before occupancy when any part of the system is inside a building (1602.5).
- Washington 1602.11.2.3: If a cross-connection is found, follow the same shutdown, disconnect, retest, 50 ppm for 24 hours chlorination, and Washington-certified laboratory procedure as for reclaimed water (Section 10.1).
Collection Surfaces and Water Quality
- 1602.9.3: Rainwater is collected from roof surfaces or other manmade, aboveground collection surfaces. Runoff from parking areas or surfaces at or below grade is treated as on-site treated nonpotable water under 1504.
- 1602.9.3.2: Overflows and bleed-off from roof-mounted equipment may not discharge onto roof areas that collect rainwater.
- 1602.9.10: A debris excluder or other approved means keeps leaves, needles, and sediment out of the tank. A roof washer, or first-flush device, diverts the initial rainfall.
- 1602.9.11: A 100-micron or finer filter is required for rainwater supplied to water closets, urinals, trap primers, and drip irrigation.
- Table 1602.9.4: Where the AHJ sets no quality standard, the table sets minimum treatment by use. Every use needs a debris excluder. Spray irrigation from storage of 360 gallons or more also needs disinfection, and where the table sets quality limits they are E. coli under 100 CFU per 100 mL and turbidity under 10 NTU. Treatment is not required for subsurface or drip irrigation, or for aboveground irrigation from storage of 360 gallons or less, beyond the debris and filter rules.
Storage Tanks (UPC 1602.9.5)
| Item | Requirement |
|---|---|
| Construction | Solid, durable, watertight, and AHJ-approved |
| Aboveground | Opaque or shielded from sunlight; accessible; on a foundation designed for the load |
| Belowground | Designed for earth loads; covers support at least 300 lb per sq ft; manholes at least 20 inches in diameter, set at least 4 inches above grade sloped away; ballasted or anchored against flotation |
| Drain and overflow | A means to drain and clean. The overflow has no shutoff valve, is at least the aggregate area of the inflow pipes, and discharges per the storm drainage rules. It gets a backwater valve if connected to storm drainage |
| Openings | Protected against insects, birds, and rodents. Access openings over 12 inches must be lockable or otherwise secured |
| Marking | Permanently marked with its capacity and a nonpotable warning |
| Venting | Where overflow or drain piping does not vent the tank, a vent of at least 1-1/2 inches, ending at least 6 inches above grade, turned down, with a 3/32-inch mesh screen |
Pumps, Pressure, and Piping
- 1602.9.6: Pumps are listed. Pumps supplying water closets, urinals, and trap primers must deliver at least 15 psi residual at the highest and most remote outlet. If pressure inside the building exceeds 80 psi, install a regulator to reduce it to 80 psi or less.
- 1602.7: Distribution piping materials meet the potable water materials rules. Gutters, downspouts, and conveyance piping meet the drainage and storm materials rules.
- 1602.9.12: Gutters keep a minimum slope and are sized per 1103.3.
- 1602.9.9: Tanks and piping subject to freezing need approved freeze protection.
- 1602.8 and 601.3: Piping has a purple background marked "CAUTION: NONPOTABLE RAINWATER WATER, DO NOT DRINK." Outside hose bibbs are allowed and are marked "CAUTION: NONPOTABLE WATER, DO NOT DRINK" (1602.9.1).
Worked Scenario
An office building will flush water closets and urinals with roof rainwater stored in a 3,000-gallon basement tank.
- Approval and permit: AHJ approval (WA 1602.1) and a permit (1601.3).
- Makeup water: potable makeup through an air gap or RP (1602.4).
- Treatment: a debris excluder and a 100-micron filter (1602.9.11), plus any additional treatment the AHJ or Table 1602.9.4 requires for flushing.
- Pump: listed, delivering 15 psi residual at the top-floor fixtures, with a regulator if pressure exceeds 80 psi.
- Tank: watertight, vented or relieved through the overflow, openings screened, and capacity marked. A belowground installation needs a secured manhole of at least 20 inches.
- Identification: purple piping and labels, with signs where required.
- Testing: a cross-connection test before occupancy, witnessed by the AHJ.
A homeowner installs an exterior rainwater tank of 300 gallons that feeds only drip irrigation. Under UPC 1601.3, is a permit required?
Only if the tank is plastic
Only if a pump is used
Yes, every rainwater system needs a permit
No; exterior systems for outdoor drip and subsurface irrigation with a maximum storage capacity of 360 gallons are exempt
A rainwater cistern that supplies water closets needs potable makeup water when the tank runs low. How must the makeup connection be protected under UPC 1602.4?
An air gap or a reduced pressure principle backflow preventer
A hose connection vacuum breaker
No protection, because rainwater is clean
A double check valve assembly
What filtration does UPC 1602.9.11 require for rainwater supplied to water closets, urinals, and trap primers?
No filter if a debris excluder is installed
A 5-micron cartridge filter
A 500-micron screen
A filter permitting passage of particulates no larger than 100 microns
Sections you finish are checked off in the contents.