Residential Sub-meter: What Is It, Why Get One?

If you use a lot of water on the outside of your home, a residential sub-meter might be right for you

If you use a lot of water only outside your home - to water the lawn or garden or fill a pool - and that water does not return to our sewerage system, you might find it cost-effective to get a sub-meter. Then the "Sewer Usage" fee on your bill would reflect only household, or inside, water consumption.

Before installing a sub-meter

Contact a Registered Master Plumber to determine any plumbing modifications that would be required to separate the household and outside water services. A WSSC Water-Registered Master Plumber must install the sub-meter.

Costs associated with installing a residential sub-meter

One-time WSSC Water Sub-meter Installation charge:

• Small sub-meter charge: $260
• Large sub-meter charge: $525
• One-time inspection Fee: $85
• Plumbing permit/Inspection Fee: $265

Additional Costs:

• System Development Charge fees may apply (Call 301-206-4003 for more information.)
• On-site plumbing work, arranged with a WSSC Water Registered Master Plumber and completed at the property owner's expense*

* WSSC Water cannot estimate this expense. The cost of on-site plumbing is negotiated between the customer/property owner and the Registered Master Plumber who will make the modifications. For further details, contact Permit Services at (301)-206-4003 (toll-free 1-800-643-8400).

WSSC Water's water consumption and sewer usage charges are based on metered public water use. This is a widely accepted practice when a utility provides both public water and sewer services. Maryland Law requires that WSSC Water shows a separate charge for Water Consumption and for Sewer Usage. The owner, tenant, or occupant who uses water "exclusively" for any purpose that does not enter the sewerage system of the WSSC Water, "shall not be charged a sewer usage charge for the water so used, provided, however, that they pay to the WSSC Water the cost of installing such a separate metered connection."

How is a sub-meter bill calculated?

Here is an example of how a WSSC Water bill is calculated to include sub-meter charges:

Main Meter registers 45,000 gallons of water (500 gallons per day) in a 90-day billing period. Sub-meter, measuring outdoor usage, registers 27,000 gallons of water used outside in a 90-day billing period.

Registered Difference between the Main Meter and the Sub-meter consumption is 18,000 gallons of water (200 gallons per day), which represents the amount used in-house and subject to Sewer Usage Charge.

The bill calculations based on this example are:

Water Consumption Rate
For water use at average daily consumption of 500 gallons: ($4.61 X 45,000)/1,000= $207.45

Sewer Usage Rate (with a Sub-Meter)
For sewer use at average daily consumption of 200 gallons: ($5.08 X 18,000)/1,000 = $91.44

Sewer Usage Rate (without a Sub-Meter)
For sewer use at average daily consumption of 500 gallons: ($6.62 X 45,000)/1,000 = $297.00