Water Supply & Distribution

Water Supply & Distribution

Learning Objectives

Upon completing this chapter, you should be able to:

1.1 Scope and General Principles

The water supply and distribution system delivers potable water from the point of service (public or private source) to fixtures and appliances throughout a building. The IPC governs the design, installation, and maintenance of these systems to ensure safe, adequate, and efficient water delivery.

Key principles embedded in the code:

The code applies to new construction, additions, alterations, and repairs. It does not apply to public water mains or treatment plants, which fall under other regulations.

1.2 Required Water Supply and Pressure

1.2.1 Minimum Pressure

The IPC requires that the water distribution system be designed to deliver a minimum pressure of 8 psi (55 kPa) at any fixture during normal flow conditions. This is the residual pressure after accounting for friction losses and elevation changes.

1.2.2 Maximum Pressure

Excessive pressure can damage fixtures, cause water hammer, and lead to leaks. The code caps the maximum static pressure at 80 psi. If the street pressure is higher, the PRV is mandatory. The valve must be accessible for servicing and located on the main supply line downstream of the meter.

1.2.3 Flow Rate and Volume

Each fixture has a minimum flow rate defined by the code (e.g., lavatory faucets, showerheads, water closets). The system must be sized to deliver these rates simultaneously based on the computed demand.

Inspection Point: Verify that a PRV is installed when the incoming static pressure exceeds 80 psi. Check that the valve is not bypassed or blocked.

1.3 Estimating Demand: Fixture Units

The IPC uses a fixture unit (FU) system to estimate peak demand. One fixture unit is a dimensionless number representing the load a fixture places on the system. The total fixture units for a building are converted to a flow rate (gallons per minute, gpm) using a table.

1.3.1 Assigning Fixture Unit Values

Each fixture type has a specific FU value based on its typical flow rate and frequency of use. For example:

These values are found in Table 403.1 of the IPC, which also lists minimum flow rates and supply pressures for each fixture.

1.3.2 Converting FU to Flow

Once the total FU is known, the corresponding demand in gpm is obtained from Table E103.3(3) (or the equivalent in the code). This table accounts for the probability of simultaneous use. For example, 20 FU might correspond to approximately 6 gpm, while 100 FU might correspond to about 20 gpm.

Note: The FU method is a statistical estimate. It does not simply add the flow rates of all fixtures; it recognizes that not all fixtures run simultaneously.

1.3.3 Continuous Flow Fixtures

For fixtures that run continuously (e.g., hose bibbs, irrigation systems, cooling tower makeup), the code requires adding the actual flow rate (in gpm) to the total demand. These are not converted to FU; they are added directly to the computed demand in gpm.

Inspection Point: Review the plumbing plans to ensure the FU totals are correctly summed and that continuous flow fixtures are included in the demand calculation.

1.4 Pipe Sizing

1.4.1 Sizing Criteria

The distribution system must be sized to:

1.4.2 Sizing Procedure

The code provides a step-by-step procedure in Appendix E (which is mandatory when adopted by the jurisdiction). The general steps are:

1.4.3 Friction Loss Tables

The IPC provides friction loss tables for various pipe materials (copper, CPVC, PEX, galvanized steel) in Appendix E or in the referenced standards. These tables list pressure drop per 100 feet of pipe for a given flow rate and pipe size.

Inspection Point: Verify that the pipe sizes on the plans match the hydraulic calculations. A common deficiency is undersizing the main trunk line while correctly sizing branch lines.

1.5 Materials and Installation

1.5.1 Approved Materials

The code lists acceptable materials for water distribution piping. Common approved materials include:

The pipe must be marked with the appropriate standard designation. Materials not listed in the code or referenced standards are not permitted unless approved by the code official.

1.5.2 Joints and Connections

Joints must be made with approved fittings and methods:

All solder and flux must be lead-free (defined as ≤ 0.2% lead content). This is a critical inspection point for potable water systems.

1.5.3 Support and Protection

1.5.4 Protection Against Freezing

All water pipes must be protected from freezing. In unheated spaces, pipes must be insulated or heat-traced. The code requires that pipes not be installed in exterior walls unless the wall is insulated and the pipe is on the warm side of the insulation.

Inspection Point: Check for lead-free solder markings on copper joints. Verify support spacing and that pipes are not resting directly on sharp edges or unprotected metal studs.

1.6 Valves and Controls

1.6.1 Main Shutoff Valve

A main shutoff valve is required on the water service pipe, inside the building, near the point of entry. It must be accessible and clearly identified.

1.6.2 Individual Fixture Shutoffs

Each fixture (except water closets in some jurisdictions) must have an accessible shutoff valve. This allows maintenance without shutting down the entire system.

1.6.3 Access Panels

Valves and other controls installed behind walls or ceilings must be accessible through an access panel of sufficient size (typically at least 12 × 12 inches).

1.6.4 Pressure-Reducing Valves

As noted, PRVs are required when static pressure exceeds 80 psi. They must be installed with a strainer upstream and a bypass (or have an integral bypass) to allow maintenance without full shutdown.

Inspection Point: Verify that all required valves are installed and accessible. A common deficiency is burying valves behind finished walls without access panels.

1.7 Protection of Potable Water Supply

1.7.1 Cross-Connection Control

A cross-connection is any physical connection between a potable water supply and a non-potable source. The code prohibits cross-connections unless an approved backflow prevention device is installed.

1.7.2 Backflow Prevention Devices

The type of device required depends on the degree of hazard:

1.7.3 Required Locations

The code mandates backflow protection at specific locations, including:

1.7.4 Testing and Maintenance

Backflow prevention assemblies (RPZ, DCV) must be tested upon installation and annually thereafter by a certified tester. Test reports must be submitted to the code official or water authority.

Inspection Point: Verify that hose bibbs have vacuum breakers installed. Check that RPZ assemblies are installed above grade, accessible, and not submerged.

1.8 Hot Water Systems

1.8.1 Supply Requirements

The code requires hot water to be supplied to all fixtures that normally use hot water (lavatories, sinks, bathtubs, showers, washing machines). The hot water supply must be capable of maintaining a temperature of at least 110°F (43°C) at the point of use.

1.8.2 Temperature Control

1.8.3 Recirculation Systems

For large buildings, a hot water recirculation system may be required to maintain temperature at distant fixtures. The code allows a maximum waiting time of 30 seconds for hot water at a fixture. If this cannot be met, a recirculation pump or point-of-use heater is required.

Inspection Point: Verify that mixing valves are installed at all shower and tub outlets. Check the T&P relief valve discharge pipe for proper termination (no threads on the end, no valve on the discharge line).

1.9 Water Hammer and Noise Control

1.9.1 Water Hammer Arrestors

The code requires water hammer arrestors where quick-closing valves (e.g., solenoid valves on dishwashers or washing machines) are installed. The arrestors must be sized per the manufacturer's specifications and installed as close to the valve as possible.

1.9.2 Pipe Noise

Pipes must be installed to minimize noise transmission. This includes:

Inspection Point: Look for water hammer arrestors at washing machine connections. Check that pipes are not tightly strapped to joists without isolation material.

1.10 Inspection and Testing

1.10.1 Hydrostatic Test

After installation, the water distribution system must be tested with water or air. The test pressure must be not less than 1.5 times the working pressure or 100 psi, whichever is greater. The system must hold this pressure for at least 15 minutes without a drop.

1.10.2 Flushing

Before connection to fixtures, the system must be thoroughly flushed to remove debris, solder flux, and other contaminants.

1.10.3 Final Inspection

The code official will inspect:

Inspection Point: Ensure the test gauge is calibrated and the test is witnessed by the inspector. Do not cover pipes or close walls until the test is passed.

Code Navigation

Use this guide to quickly locate topics in the IPC during the exam:

Practical Inspection Points (Summary)

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