6.1 Cross-Connection Fundamentals, Hazard Classes & Pressure Conditions
Key Takeaways
High versus low hazard is based on how a toxic or nontoxic solution is intended by its manufacturer to interface with the potable water supply.
Continuous pressure means pressure above atmospheric in the water supply for more than 12 continuous hours; anything less is noncontinuous.
Any connection to the drain system or to piping carrying water from nonpotable sources, every hose-threaded or serrated outlet, maintenance sinks in public buildings and chemical feeders are high hazard situations.
Hose outlets used only for draining the system, for individual residential clothes washers or dryers, or for lockable-box dialysis machines are not cross connections.
A multipurpose piping system in a one- or 2-family dwelling built of water distribution materials and joints is not a cross connection (SPS 382.41 (3) (b) 7.).
Why cross-connection control is a code issue
A cross connection is any physical link through which a nonpotable liquid, solid or gas could enter the potable water system. Backflow is the reverse flow that makes the link dangerous. SPS 382.41 (3) requires water supply systems, and the connection of every fixture, appliance, piece of equipment and nonpotable piping system, to be designed, installed and maintained to prevent contamination through cross connections. A code note in SPS 382.22 states plainly that "a cross connection is considered a health hazard by the department." The water supplier also has duties: NR 810.15 (1) requires community water systems to run a comprehensive cross connection control program.
The three classifications (SPS 382.41 (3) (b))
1. Hazard
"The designation of a high hazard or low hazard situation shall be determined on the basis of how a toxic or nontoxic solution is intended or recommended by the manufacturer of the solution to interface with the potable water supply system." Hazard depends on what could flow back, not on how likely it is to happen.
2. Pressure
| Condition | Definition |
|---|---|
| Continuous pressure | Pressure greater than atmospheric exists in the water supply system for more than 12 continuous hours |
| Noncontinuous pressure | Anything that does not meet the 12-hour test |
A supply line with a downstream shutoff valve that stays closed overnight is under continuous pressure. A device that only sees pressure while a faucet is open is noncontinuous. This matters because atmospheric vacuum breakers may never be under continuous pressure.
3. Backpressure versus back-siphonage
Table 382.41-1 sorts every situation into backpressure (downstream pressure higher than supply pressure, such as a boiler, pump or elevated tank) or back-siphonage (negative supply pressure, such as a main break or fire-flow drawdown, pulling water backward). Some devices handle only back-siphonage.
Situations the code declares high hazard
A high hazard cross connection exists at a connection of the water supply to:
- Any part of the drain system (emergency fixtures aside).
- Any piping carrying water from nonpotable sources, such as lakes, rivers, streams or creeks.
It also exists at (SPS 382.41 (3) (b) 4.):
- Any hose bibb, faucet, wall hydrant, sill cock or other outlet ending in hose threads
- Any outlet ending in a serrated nipple that accepts a hose
- Faucets and outlets serving a building maintenance sink in a public building
- A chemical pot-feeder or automatic chemical feeder serving a boiler, cooling tower or chilled water system
- Piping connected to a fire hydrant outlet for any purpose other than firefighting
Connecting two systems, one fed by a public supply and one fed by a private well, is also high hazard. The interconnection itself needs DNR approval under NR 811.
Not cross connections
- A hose-threaded outlet installed solely to drain the water supply system, to connect an individual residential clothes washer or dryer, or to connect an individual portable dialysis machine in a lockable box.
- A multipurpose piping system serving a one- or 2-family dwelling, when the sprinkler piping uses water distribution materials and joints under SPS 384.30 (4) (e) and 384.40.
- An emergency fixture (eyewash, drench shower) unless its outlet can be submerged in a fixture. If it can be submerged, it is a low hazard situation.
Containment in addition to isolation (SPS 382.41 (3) (c))
Wisconsin protects at the point of use (isolation). For some facilities it also requires a containment assembly protecting the whole supply:
- Sewage treatment facilities subject to NR 110: an RP (reduced pressure principle) or RPDA (reduced pressure detector) assembly in each building's water service, in the private water main upstream of all services, or upstream of all outlets and process piping in a shared building.
- Marinas, wharves and docks serving boats: an RP or RPDA in the water supply.
A containment assembly never replaces the protection required at each fixture, appliance or piping system (3) (c) 3.
Prohibitions (SPS 382.41 (3) (d))
- A toxic solution may not be used as the heat-transfer fluid in a single-wall heat exchanger for potable water. A code note says an HT-1 rated fluid under the NSF Nonfood Compounds program (21 CFR 178.3570) counts as nontoxic.
- A cross connection control method, device or assembly may not be bypassed without another of at least equal protection.
Existing fire sprinkler systems (SPS 382.41 (3) (e))
Altering an existing automatic sprinkler system triggers full compliance when the existing supply line is increased in diameter or an existing cross-connection method is removed or replaced. Sprinkler backflow assemblies must also be listed for fire protection use.
Worked classification examples
| Connection | Hazard | Pressure | Condition |
|---|---|---|---|
| Lawn irrigation zone with a fertilizer injector | High | Depends on valve location | Back-siphonage, plus backpressure if pumped or elevated |
| Boiler makeup water with an automatic chemical feeder | High (chemical feeder) | Continuous | Backpressure |
| Water softener drain line to a standpipe | High (connection to the drain system) | Noncontinuous at the drain | Protected by an air gap or a vacuum breaker tee |
| Kitchen faucet with a hose-thread aerator | High (hose threads) | Noncontinuous | Back-siphonage |
Section 6.2 shows which device Table 382.41-1 allows for each combination.
Under SPS 382.41 (3) (b) 2., when does a continuous pressure situation exist?
When pressure is above atmospheric for more than 12 continuous hours
When pressure exceeds 80 psig
When the device is downstream of a pump
When pressure is present for more than 1 hour
Which outlet does SPS 382.41 (3) (b) 5. say is NOT a cross connection?
A hose bibb on the outside of a house
A laundry faucet with a hose-thread outlet used for a garden hose
A service sink faucet in a public building
A hose-threaded outlet installed solely to connect an individual residential clothes washer
How does Wisconsin determine whether a cross connection is high hazard or low hazard?
By the pipe size and the static pressure at the point of connection
By how the solution's manufacturer intends it to interface with potable water
By the building occupancy classification under the commercial building code
By whether the connection is above or below the flood level rim of the fixture
Sections you finish are checked off in the contents.