9.2 Backflow Prevention & Cross-Connection

9.2 Backflow Prevention & Cross-Connection

Quick Answer: Keep potable water from drinking sewage, chemicals, irrigation, or boiler water. 248 CMR 10.14(7)(c) makes MassDEP or its designee the authority for the type of cross-connection control, to the last free-flowing outlet. An RPZ or double-check valve assembly does not get a plumbing permit until a DEP or designee approval letter is on the application. On the fixture side, 10.14 lists air gaps (Table 7), atmospheric and pressure vacuum breakers, RPZ, DCVA, and BPIAV devices in Table 11. Mortuary-table hoses stop 12 inches off the table. Non-potable pumps prime through an air gap only. This section teaches those listed protections. It does not invent a containment-versus-isolation scheme the code does not define.

This is the second of the PSI six-item Water Supply cluster. Independent OpenExamPrep teaching below follows 248 CMR 10.14 (Cornell and the Mass.gov 12/8/2023 PDF) and the MassDEP cross-connection program at 310 CMR 22.22 and M.G.L. c. 111, § 160A as 10.14 itself cites them.

Two programs, one potable pipe

248 CMR 10.14(7)(a) requires the potable system to be designed, installed, and maintained so non-potable liquids, solids, or gases cannot enter through cross-connections or other piping connections. 10.14(7)(c)3. then assigns DEP or its designee as the authority having jurisdiction for the type of cross-connection control required, and for preventing contamination to the last free-flowing outlet or consumer’s tap. 10.14(7)(c)2. is the permit lock: no plumbing permit for installations that require Reduced Pressure Zone Backflow Preventers or Double Check Valve Assemblies until the application includes a letter of approval from MassDEP or its designee.

That split is the exam distinction. The plumbing inspector enforces 248 CMR device installation, labeling, air gaps, vacuum-breaker critical levels, and Product-accepted hardware. MassDEP / the public water supplier decides, under 310 CMR 22.22, which RPZ or DCVA (and related high-hazard assemblies) belong on a surveyed facility, and they issue the letter the inspector must see. 310 CMR 22.22 also states that atmospheric breakers, pressure vacuum breakers, backflow preventers with intermediate atmospheric vent, dual check valve preventers, and hose-connection vacuum breakers used for certain low-hazard applications referred to in the State Plumbing Code are those meeting Board of State Examiners requirements. 248 CMR 10.14 Table 11’s named columns are AG, RPBP, DCVA, AVB, PVB, and BPIAV. Teach those names. Do not add an unpublished “containment device versus isolation device” lecture; 10.14 does not define those two words as a ranking system.

Where potable and non-potable piping share a building, 10.14(7)(b) requires labels or paint at least every 10 feet, at direction changes, on each side of a penetration, and at every shut-off. Potable is color-coded green with black lettering “safe water.” Non-potable is yellow with “unsafe water.” Lettering is at least the pipe diameter, capped at two inches for piping larger than two inches. Non-potable outlets are identified at each outlet. Piping after a backflow device is labeled “Water Subject to Questionable Safety.”

Individual wells shall not interconnect with a public potable supply unless MassDEP specifically approves. Two public supplies interconnect only with approval of the health authority having jurisdiction (10.14(7)(d)).

Air gaps — Table 7

An air gap is measured vertically from the lowest end of the potable outlet to the flood rim of the fixture or receptacle. The general rule in 10.14(7)(l)1.a. is twice the effective opening, or three times the effective opening if the outlet is closer to a wall or similar vertical surface than three times the opening. In no case less than Table 7:

If the outlet can be submerged and cannot keep that air gap, install an approved backflow preventer or vacuum breaker (10.14(7)(l)2.).

Vacuum breakers, RPZ, double-check, and BPIAV

Atmospheric vacuum breaker (10.14(7)(l)3.a.). Critical level at least six inches above the flood-level rim, on the discharge side of the last control valve. No shut-off valve or faucet beyond the vacuum breaker. For closed equipment such as a pressure sterilizer, treat the top of the vessel as the flood rim and install a check valve on the discharge side of the vacuum breaker.

Pressure-type vacuum breaker (10.14(7)(l)7.). For connections not subject to backpressure, critical level a minimum of 12 inches above the highest outlet or fixture served.

Reduced pressure zone backflow preventer (10.14(7)(l)3.b.). May be installed subject to full static pressure. Where the vent port could damage the building, take precautions. This is a high-hazard assembly in Table 11 for sewage plants, hospitals/mortuaries/clinics, plating, radioactive material, commercial laundries, high-pressure boilers with chemicals, and similar rows — look up the row rather than memorizing every X.

Double check valve assembly (DCVA). Table 11’s double-check column is the 10.14 name for that assembly. 10.14(7)(c) pairs it with RPZ for the DEP-letter permit lock. Refrigerating condensers or cooling jackets that do not have two metal thicknesses between toxic refrigerant and potable water get an approved double-check installation, plus a relief valve set five PSIG above maximum water pressure if the unit contains more than 20 pounds of refrigerant (10.14(7)(i)).

BPIAV is Table 11’s backflow preventer with intermediate atmospheric vent. Low-pressure heating boilers that are residential or small commercial with no chemicals added list air gap or BPIAV. High- and low-pressure boilers with chemicals list air gap or RPBP. Self-feeding potable connections to a heating boiler need an approved backflow preventer or air gap, except manually controlled supplies to residential-type steam and/or gravity-fed hot-water space-heating systems, which 10.14(7)(g)2. does not require a backflow preventer on.

Devices of all types are accessible, preferably in the same room as the fixture, or in a readily accessible utility space (10.14(7)(l)3.c.).

A 35-foot barometric loop may substitute, in the limited 10.14(7)(l)6. case, for devices on connections not subject to backpressure. That is a listed alternative, not a field invention.

Lawn irrigation, hoses, bidets, mortuary tables, pumps

Table 10 / C-L settings (Cornell Table 10; some PDF extracts reprint it as Table 8 — use the fixture row, not the header number if the print is scrambled):

Table 11 irrigation row: evaluate each case. AVB only if no backpressure is possible and no health hazard exists. PVB if backpressure is possible. AG and RPBP are also listed. That is why a lawn job is not “any vacuum breaker anywhere.”

Hose threads. 10.14(3)(k)3. requires a backflow preventer or vacuum breaker on all sillcocks, hose connections, and wall hydrants, including faucets with a hose-thread outlet. Table 11 row 5 adds that fixtures with hose-thread inlets, in addition to an air gap, shall at a minimum have an AVB. Residential outside hose connections are no more than 100 feet apart; commercial buildings need sillcocks only in mechanical rooms, penthouses, or similar mechanical areas.

Bidets are named in 10.14(7)(h) as connections that shall be protected against backflow. The section does not pick a single Table 11 column for every bidet. Protect the bidet with a listed 10.14 method (air gap or Product-accepted backflow device as the installation requires). Do not invent an RPZ-for-every-bidet rule that Table 11 does not print.

Operating, dissection, embalming, and mortuary tables: the hose used for water supply shall terminate at least 12 inches away from every point of the table or attachments (10.14(7)(h)2.). Hospitals, mortuaries, and clinics are an AG / RPBP Table 11 row for the premise hazard — that is separate from the 12-inch hose termination at the table.

Pumps for non-potable water, chemicals, or other substances: priming connections may be made only through an air gap (10.14(7)(h)3.). Building drainage, sewer, or vent systems are in the same protected-connection list.

Chemical cleaning dispensers. Hard-piped units need a plumbing permit; the public water supplier names the backflow device. Hose-end dispensers do not need a plumbing permit but need an air gap or ASSE 1055B listing, plus a pressure bleeder that visually free-flows to a sink or drain through a one-piece quick-disconnect assembly that will not let the bleeder be removed from the disconnect.

Cooling water returns to the drainage system through an air-gapped indirect waste and shall not return to the potable system (10.14(7)(k)). Gray-water or black-water reuse needs Special-permission under 248 CMR 3.04(3) unless the system is already Product-accepted.

Scenario. A funeral home in Springfield needs a new embalming table. The water hose cannot drape onto the table; it stops 12 inches away. The premise is a Table 11 hospital/mortuary/clinic hazard, so the RPZ path includes a DEP letter before the plumbing permit. A landscaper’s lawn manifold that can see pump backpressure is a PVB or RPZ evaluation, not an AVB six inches under the highest head.

Official resources

• 248 CMR 10.14 (Cornell) — 10.14(7), Table 7, vacuum-breaker C-L, Table 11
• Policies, regulations, and statutes for plumbers and gas fitters
• MassDEP 310 CMR 22.22 cross-connection regulations — RPZ/DCVA testing and Board-approved low-hazard devices
• M.G.L. c. 111, § 160A — as cited by 10.14 for potable-supply protection