Water Service Sizing


The water service supply line delivers potable water to your home from the village water main. The water service line for a residential home is typically a ¾” to 1” pipe that can be seen entering your building near the water meter. If you are proposing to add plumbing fixtures such as a new shower, new sink, new toilet or similar, it is required by the Illinois Plumbing Code that the water service supply line is large enough to accommodate the capacity of water that is demanded from all of your plumbing fixtures combined as established in Table N (Flush Tank) or TABLE O (Flushometer) of the Illinois Plumbing Code. At an existing residence, several conditions can affect the capacity of the water service line including pipe size, length of water service line and condition of the pipe. To determine if the existing water service supply line is adequately sized you will need three pieces of information:

TABLE A - Water Service Line-Sizing Worksheet - is attached and allows you to calculate the number of existing and proposed plumbing fixtures within your home as well as any possible future plumbing fixtures. For each fixture, there is a corresponding Water Supply Fixture Unit (WSFU). The worksheet will allow you to calculate the total WSFU’s by multiplying in each row the number of fixtures by the WSFU’s and then adding all the WSFU’s in the right-hand column. The total will then be compared to TABLE N or TABLE O.

TABLE N or TABLE O - from the Illinois Plumbing Code and identifies the minimum water service line or “pipe size” (third column) based on the total number of WSFU’s calculated from TABLE A. Please Note: TABLE N should be referenced if toilets are tank type and TABLE O should be referenced if toilets are flushometer type.

PIPE SIZE - of the existing water service line to your home is best determined by measuring the pipe where it enters the building. You may also call the Niles Water Division, who may be able to confirm the size of the existing water service line.

If the proposed addition of plumbing fixtures to an existing residence results in more fixtures than supported by the water service as determined by TABLE N/O the capacity of the water service line is undersized and does not comply with Illinois Code. 


Option 1 - Replacement. If the proposed addition of plumbing fixtures to an existing residence results in more fixtures than supported by the water service line, the line shall be replaced from the Village water main to the meter. Prior to commencing the installation of any new, repair or replacement of any existing water service line a permit is required to be issued by the Niles Building Department or

Option 2 - Pressure Test. If the proposed addition of plumbing fixtures to an existing residence results in more fixtures than supported by the water service line the capacity of the water service line can be evaluated by an alternate method and that is by having your plumber perform a pressure test. The pressure test may have been stipulated when the Building Department issued the building permit to you. Section 890.1210c of the Plumbing Code requires a minimum constant water pressure on the discharge side of the water meter to be at least 20 p.s.i. The water distribution system must be adequately sized to provide a minimum constant water pressure at each fixture of at least 8 p.s.i. The pressure test is conducted after the installation of the additional fixtures and must be conducted by a registered plumbing contractor and witnessed by the Village of Niles registered plumbing inspector.

The pressure test shall be conducted as follows:

Notify the Building Department at least one day in advance that you will be performing a pressure test with your Plumbing Contractor and pay $40.00 to have the Village Plumbing Inspector witness the pressure test. Pressure tests are typically scheduled on each Tuesday at approximately 9:00 a.m. Pressure tests shall be performed no sooner than after the plumbing rough inspection and can be done on the same day as the final plumbing inspection.

On the day of the pressure test: locate all water outlets and toilets in the house.

Find the sill cock or drain cock located closest to the water meter and attach the pressure gauge. Open the sill cock fully and record the static pressure.

Turn on all plumbing fixtures, both hot and cold. Start in the basement, if applicable, and work up to the top floor. Do not open other sill cocks or yard hydrant.

Flush all toilets and record the residual pressure while the toilets are still filling.

If the pressure falls below 20 p.s.i., the water service must be replaced, see Option 1 above. If the pressure test finds that the water pressure at the water service entrance is maintained at no less than the 20 p.s.i. at peak demand, the water service line size complies with State Plumbing Code and does not need to be replaced. Money that was collected by the Village for the installation of the proposed new water service line may be eligible for a refund. These fees may include costs for a larger water meter, inspection fees, cost for replacement of a water service line from main to B-box, deposits and others. To initiate a refund send a copy of the inspection report that indicates the pressure at the water meter exceeds the required State Plumbing Code pressure to the Community Development Department. The Water Division will review your request, identify all fees that can be refunded and will then forward the information to the Finance Department for processing of the refund.