1.2 Service Connections & Meters

Service Connection Components

The service connection is the segment of the distribution system that links the public water main to the customer's private plumbing. It consists of several key components, each serving a specific function in flow control and isolation.

The Corporation Stop (Corp Stop) is the first valve in the service connection. It is installed directly on the water main, often while the main is still under pressure (a process known as tapping or hot tapping). The corp stop allows operators to turn the water supply to the service line on or off right at the main. It is typically buried and rarely operated after the initial installation unless a major repair on the service line is required.

The Service Line is the pipe that carries water from the corp stop to the customer's property. Historically, materials like lead and galvanized iron were used, but modern installations predominantly use copper (Type K is standard for underground water service due to its thickness) or plastics like High-Density Polyethylene (HDPE) or Cross-linked Polyethylene (PEX). The choice of material depends on local codes, soil conditions, and the potential for freezing.

The Curb Stop is a valve located near the property line, typically between the curb and the sidewalk. Unlike the corp stop, the curb stop is accessible from the surface via a vertical pipe called a curb box. This valve allows the utility to turn the customer's water on or off without needing to access the customer's home or dig up the street. It is used for turning off service due to non-payment, stopping flow during a plumbing emergency inside the home, or isolating the property when changing the water meter.

Water Meters

Water meters are essential for equitable billing, detecting leaks, and tracking overall system demand. Selecting the correct meter type and size is critical for accurate measurement.

Displacement Meters

Displacement meters, specifically positive displacement meters, measure water volume by dividing the flow into small, fixed volumes and counting them. The most common type is the nutating disc meter. As water flows through the measuring chamber, it causes a disc to wobble (nutate), turning a spindle that drives the register.

Displacement meters are highly accurate at low flow rates, making them the standard choice for residential applications (typically 5/8-inch to 1-inch sizes). However, they restrict flow significantly and can cause excessive head loss if subjected to high flow rates. They are also sensitive to particulate matter, which can jam the moving parts.

Velocity Meters

Velocity meters measure the speed of the water flowing through a pipe of known cross-sectional area to calculate volume. The most common type is the turbine meter, which uses a rotor that spins at a speed proportional to the water velocity.

Velocity meters are ideal for high-volume, continuous flow applications, such as large commercial buildings, industrial facilities, or wholesale connections between utilities. They offer very little resistance to flow (low head loss). However, their primary drawback is that they are notoriously inaccurate at low flow rates because low velocities may not generate enough force to turn the rotor reliably.

Compound Meters

In situations where a facility experiences both very high and very low flows (e.g., a hotel, an apartment complex, or a school), neither a displacement nor a velocity meter alone is adequate. A compound meter solves this problem by integrating both types of meters into a single unit, along with a pressure-regulating valve.

During periods of low flow, the valve directs water through the smaller displacement meter, ensuring accurate measurement. When demand increases and flow reaches a certain threshold, the pressure drops, causing the valve to open and direct the bulk of the water through the larger velocity meter. The readings from both meters are added together to determine total consumption.

Meter Sizing, Testing, and Maintenance

Properly sizing a meter is just as important as selecting the right type. A meter that is too large for the application will fail to accurately measure low flows, resulting in lost revenue for the utility (unaccounted-for water). Conversely, a meter that is too small will cause excessive pressure drop and wear out prematurely due to operating consistently near its maximum capacity.

All mechanical meters degrade over time, typically resulting in under-registering (measuring less water than actually passed through). Therefore, utilities must establish a regular testing and replacement schedule.

• Residential meters (5/8" to 1") should typically be tested or replaced every 10 to 15 years, or after a specific volume has been registered.
• Large commercial meters and compound meters, which represent a significant portion of utility revenue, should be tested much more frequently, often annually or bi-annually. Testing is usually performed in the field using a calibrated bypass testing apparatus to compare the meter's reading against a known standard.