9.1 Water Supply Materials, WSFU & Sizing

9.1 Water Supply Materials, WSFU & Sizing

Quick Answer: Size Massachusetts building water piping from 248 CMR 10.14 Tables 1, 2, and 3: add Factor Values, multiply by the occupancy Demand Factor, then pick the Capacity Value pipe. That is the Massachusetts load method; it is not an IPC water-supply fixture-unit table. Install only 248 CMR 10.06 Table 2 water-distribution materials that are also Board Product-accepted. Type K and Type L copper are listed A/A above and below ground. PEX and CPVC are listed A/A but only where 10.06(2)(f) allows them, and never within 24 inches of the final connection to a domestic water heater. Galvanized steel and Type M copper are not on Table 2. Put a full-port main control on the meter discharge (or on the service if there is no meter). If outlet pressure exceeds 80 PSIG, add a reducing valve and a 0–150 PSIG gauge within 24 inches downstream.

The PSI Candidate Information Bulletin dated October 3, 2025 groups Water Supply / Materials, Backflow Prevention, and Water Temperatures as a six-item written cluster. This section is the materials-and-sizing third of that cluster. It is independent teaching for the Massachusetts journeyman plumber exam. It is not a Board publication and it does not claim official approval.

Do not size a Worcester two-family from an IPC appendix. 248 CMR 10.14(2)(a) says the cold-water supply from the meter or main control valve to branches, risers, and fixture connections is based on the total demand in 10.14. Sizing of the building water main, branch distribution, risers, and fixture supply uses Tables 1, 2, and 3, unless a Massachusetts professional engineer designs the system. A demand factor from Table 2 is applied to find the minimum diameter of the building main and water-distribution piping.

Materials: Table 2, not a catalog page

248 CMR 10.06(1)(a) and 248 CMR 3.04 still require Board Product-accepted products. 10.06(2)(e) then sends water-distribution pipe and fittings, above and below ground, to Table 2. The Mass.gov 248 CMR 10.00 PDF effective December 8, 2023 prints that table. Verified rows that matter on this exam:

Type M copper (red) and galvanized steel do not appear on Table 2. Galvanized schedule 40 with drainage-pattern fittings appears on 10.06 Table 1 for DWV, not as a new water-distribution material. Do not treat an old “replacement only” galvanized water sentence from a withdrawn draft as live Table 2 permission. If an existing galvanized water line is being extended, 10.06(1)(b) lets the Inspector allow like grade or quality only where the original installation met the code then in effect — that is renovation matching, not a license to rough a new house in galvanized water pipe.

Potable pipe, valves, and fittings anticipated for human consumption must also meet the federal Safe Drinking Water Act, 42 U.S.C. § 300f (248 CMR 10.06(1)(e) and 10.14(1)). Used piping that once carried anything other than potable water shall not be reused for potable water (10.14(7)(f)).

Water service pipe is defined in 248 CMR 10.03 as the pipe from the municipal main or other source to the building water-distribution system. Table 3 capacity values cover service, mains, risers, and/or branches. Do not invent a separate unpublished municipal material list; install Product-accepted Table 2 materials on the building distribution and follow the water supplier on the public-side service when that supplier’s specification is part of the job.

PEX, CPVC, six stories, and the 24-inch heater rule

248 CMR 10.06(2)(f) is the overlay Table 2 points to. CPVC and PEX may be used for hot and cold water that is:

1. in residential dwellings, hotels, motels, inns, condominiums, and similar buildings not exceeding six stories; or
2. in a predominantly residential building with a single non-residential use on a single floor, that use categorized exclusively as employee (non-residential) under 248 CMR 10.10(15) Table 1, limited to a maximum of four plumbing fixtures, and limited to toilets, lavatory / residential / service sinks, and drinking water stations; or
3. dedicated cold water from the outlet of the water meter or main control valve inside any building directly to drinking water stations; or
4. PEX in commercial buildings conveying reverse-osmosis or similar purified water from treatment to drinking points of use.

Exceptions. CPVC and/or PEX domestic water tubing shall not be installed within 24 inches of the final connection to any domestic water heater. CPVC and PEX shall not be used for steam flushing of water-purification systems; only Type 316 stainless steel tube and fittings serve that duty.

The Mass.gov policies list still carries CPVC in 6 Story Buildings (Board interpretation enacted 05-28-2014, posted 12/07/2017). The Board reads the older “six stories or 60 feet” language this way: CPVC may be used if the building is six stories high as stated on the building permit, even if the building is higher than 60 feet. Current 10.06(2)(f) says not exceeding six stories and no longer prints the 60-foot alternative. On the exam, count stories on the permit, not a tape-measure argument that a six-story hotel is “too tall” at 65 feet.

Scenario. A six-story Lowell condominium on the building permit is a CPVC/PEX building under 10.06(2)(f)1., but the last 24 inches onto the water heater are copper or another Table 2 metal that the heater connection allows. An eight-story office is not a 10.06(2)(f)1. building; dedicated cold PEX to drinking stations under (f)3. or purified-water PEX under (f)4. is a different, narrower permission.

Factor Values, Demand Factors, and a small worked example

PSI outlines often say WSFU. Massachusetts does not publish an IPC-style water-supply fixture-unit table in 10.14. Table 1 is Minimum Sizes of Individual Fixture Branches and Factor Values. Cornell LII’s HTML table of that same 12/8/2023 section lists these verified pairs (nominal branch size, Factor Value):

The individual fixture branch extends to the fixture connector and ends in a fixture shut-off. Fixture connectors shall not exceed 30 inches and shall be Product-accepted, except dishwashers, washing machines, and icemakers (10.14(2)(a)7.).

Table 2 Demand Factors (Mass.gov 12/8/2023 PDF): one- or two-family dwelling 0.50; multi-residential 0.35; hotel 0.70; school general 0.75; school shower room 1.00; institutional general 0.45; assembly general 0.25; restaurant/café 0.70; club house 0.60; business and mercantile general 0.25; laundry 1.00; industrial exclusive of process piping 0.90.

Table 3 Capacity Values: 1/2 in. 1 to 4; 3/4 in. 4.1 to 9; 1 in. 9.1 to 16.5; 1-1/4 in. 16.6 to 28; 1-1/2 in. 28.1 to 55; 2 in. 55.1 to 107.5 (larger sizes continue in the table — look them up rather than guessing).

Worked example (verified Table values only). One-family dwelling. Fixtures: one tank toilet (Factor 1, cold), one lavatory (1 hot + 1 cold), one residential kitchen sink (2 + 2), one single-head shower (2 + 2). Total Factor Value = 11. Table 2 demand factor 0.50. Capacity Value = 11 × 0.50 = 5.5. Table 3 places 5.5 in 4.1 to 9, so the cold-water main in this method is 3/4 inch. A Capacity Value of 4.0 would still sit in the 1/2-inch band (1 to 4); 4.1 is the 3/4-inch start. The code’s own published example for a larger one-family fixture set totals Factor 28, times 0.50, Capacity 14.0, which lands in 9.1 to 16.5 and equals one-inch pipe. Do not import IPC WSFU numbers into either example.

Meter, pressure, and what the inspector looks for

Main control valve (10.14(3)(b)). Full-port, on the discharge side of each water meter, or on the incoming service where no meter is present, not less than the size of the building water service. A draw-off is installed upstream of the main control on the meter discharge. An accessible drain valve is required upstream and near the meter or main control. In other than single-family homes, drain valves at low points so the system can be emptied. Dead ends are not allowed. Risers serving multiple fixtures above the first floor get a full-port valve at the base and a draw-off upstream of that riser valve. Multiple dwelling units need a control so one unit can be shut without stopping water to others, accessible from the unit served.

Pressure. Table 4 minimum flow pressures include 8 PSI at most faucets, tubs, residential laundry, shower heads, and tank toilets; 15–20 PSI at a flushometer toilet; 15 PSI at a flushometer urinal; 10 PSI at an outside faucet. Maximum flow rates in the same table include residential lavatory 1.5 GPM, non-residential lavatory 0.5 GPM, residential kitchen/bar 2.2 GPM, shower head 2 GPM (except emergency showers in 10.10(12)), tank toilet 1.28 GPM. If street or service pressure cannot make those fixture pressures, install a booster: a properly sized booster in one-, two-, and three-family dwellings; a Massachusetts PE design in other buildings. If pressure at a fixture, device, or appurtenance exceeds 80 PSIG, install a reducing valve upstream of that device and a 0–150 PSIG gauge within 24 inches downstream. Exception: water-service piping upstream and downstream of a water-pressure booster.

Rough water testing under 248 CMR 10.04 is not less than 125 PSI from a potable source (air or inert gas may be used). When the Inspector requires disinfection, 10.14(4) lists 50 ppm / six hours or 100 ppm / two hours, then flush.

Saddle valves are prohibited. Do not tap, burn, weld, or drill a water line except with Board Product-accepted mechanical devices engineered for that penetration.

Official resources

• 248 CMR 10.14 Water Supply and the Distribution System (Cornell) — Tables 1–4, meter valve, 80 PSIG rule
• 248 CMR 10.06 Materials (Cornell) — Table 2 and 10.06(2)(f) PEX/CPVC
• 248 CMR 10.00 Uniform State Plumbing Code (Mass.gov, effective 12/8/2023) — official PDF tables
• CPVC in 6 Story Buildings — permit stories, not a 60-foot tape