Multifamily Water Submetering

In most multi-unit residential buildings, one utility meter serves every apartment and the owner pays the bill. Water and sewer are then either absorbed into rent or recovered with an estimate. Multifamily water submetering replaces the estimate with a measurement: a meter on each unit's supply, read remotely, with each resident billed for their own use. This page is part of our submetering guide.

Why owners submeter apartment water

• Cost recovery. Water and sewer are among the largest controllable operating costs in multifamily property, and they rise every year.
• Behaviour. Residents who see their own consumption on a bill have a reason to report a running toilet or a dripping tap.
• Leak detection. A unit with continuous flow at 3 a.m. has a leak. A building meter cannot tell you which unit; apartment meters can.
• Fairness. A single occupant in a one-bedroom stops subsidising a family of five next door.

What an unseen leak costs

Rates vary by jurisdiction — substitute your own combined water and sewer rate per ccf and the arithmetic holds. One ccf is 748.05 gallons. A 0.1 gpm flow is about six gallons an hour: a weeping valve or a running fill that nobody notices, and that a quarterly bill cannot distinguish from normal use. On an interval record it shows up as a baseline that never returns to zero overnight.

For the distinction between utility-owned and owner-side meters, see who owns your water meter in New York City.

RUBS vs true submetering

A ratio utility billing system (RUBS) divides the building's water bill using a formula — floor area, number of occupants, number of bedrooms, or a combination. It needs no hardware and can start immediately. Its weakness is that a resident's bill barely changes whatever they do, so it recovers cost without changing consumption, and it gives no information about where water is going.

True submetering measures each unit. It costs hardware and installation up front, but it links bills to use, gives residents a reason to conserve, and turns every apartment into a leak detector. Many owners use RUBS for common-area water such as irrigation and laundry and submeters for the units themselves. Either way, local rules on how utility charges may be calculated and disclosed apply — check them before choosing.

What the install involves on existing plumbing

The deciding factor is plumbing layout, not the meter. Walk the building before pricing.

• One supply per unit. Newer buildings, and many garden-style buildings, feed each apartment from a single line with a shutoff. One meter per unit goes at that point.
• Multiple risers per unit. Older mid-rise buildings often run several vertical risers, each serving the kitchen or bathroom of a stack of units. Each unit then needs a meter on every riser branch that feeds it, which multiplies hardware.
• Hot and cold. Where hot water comes from a central plant, meter cold and hot separately, or meter cold only and allocate hot water — hot water meters need a temperature rating to match.
• Access. Meters must be reachable for service; behind a finished wall needs an access panel.
• Cut-in or clamp-on. Mechanical meters are cut into the line by a licensed plumber with a short shutdown per unit. Clamp-on ultrasonic meters avoid cutting the pipe and suit larger lines and common-area branches.

Which meters fit multifamily water submetering

Apartment supply lines are typically 5/8" to 1". Small-bore positive displacement and multi-jet meters with pulse output are the usual choice; ultrasonic meters suit larger lines and retrofits where cutting the pipe is a problem.

• Positive displacement (cold water): M-E PD 5/8" x 3/4" lead-free bronze with pulse, M-E PD 3/4" x 3/4", M-E PD 1", and the MTW Poly PD19 5/8" x 3/4".
• Multi-jet: M-E MJ 5/8" x 3/4", M-E MJ 3/4" x 3/4", MTW MJ20 5/8" x 3/4".
• Hot water: MTW MJ420S hot 5/8" x 3/4" and the MTW CAS hot water meters.
• Ultrasonic (larger lines, clamp-on): EES-101 ultrasonic water submeter and the higher-precision EES-201.

See every option in water meters and ultrasonic flow meters.

Low-flow sensitivity is the specification that matters

A meter that cannot resolve roughly 0.1 gpm cannot find a $974-a-year leak, regardless of its accuracy class at rated flow. For leak detection, low-flow sensitivity matters more than accuracy class.

Two pulse inputs on a typical gateway will not carry gas plus water. If both are in scope, a pulse or Modbus concentrator belongs in the design rather than being added later.

Reading the meters and billing

Manual reading of dozens of meters every month does not last. Pulse outputs from each meter are counted by a data collector — a high-density pulse module wired to a group of meters, or a wireless transceiver such as the ModHopper where running cable to every unit is impractical. Readings are uploaded on a schedule and used to produce each unit's charge.

• Bill on a fixed read date and keep raw interval data so disputes can be checked.
• Reconcile the sum of unit meters against the building meter; the gap is common-area use and leaks.
• Set a continuous-flow alert per unit so leaks are caught before the bill.
• Follow local rules on disclosure, fees and how charges are calculated.

The full chain from meter to bill is described on utility submetering systems.

What water submetering does not do

Water savings do not improve a building's Local Law 97 position. Emissions from treating and conveying municipal water sit with the water utility, upstream of the building — Scope 3 for the building owner. Water submetering pays back on the water and sewer bill, which is a sound case on its own. Presenting it as carbon compliance relief would not survive review.