Water Supply Systems

Water Supply Systems

Chapter Introduction

This chapter covers all the knowledge required for the Red Seal exam concerning potable water supply systems in residential, commercial, and institutional buildings. You must master hydraulic principles, sizing methods, applicable Canadian standards, and installation procedures. This chapter is structured to follow the logic of the trade: from the supply source to the point of use, including load calculations, material selection, and regulatory requirements.

Fundamental Principles of Applied Hydraulics

Pressure, Flow Rate, and Velocity

Pressure in a water supply system is expressed in kilopascals (kPa) in Canada. Static pressure is the pressure measured when water is at rest; dynamic pressure is the pressure measured under flow conditions. The fundamental relationship between pressure, flow rate, and velocity is governed by the continuity equation:

Q = A × V

Where Q is the flow rate (L/s or m³/s), A is the cross-sectional area of the pipe (m²), and V is the average water velocity (m/s).

The available pressure at any given point in the system is the static pressure minus the pressure losses due to friction, changes in direction, and fittings. The total head loss (ΔP) in a pipeline is calculated using the Darcy-Weisbach equation:

ΔP = f × (L/D) × (ρV²/2)

Where f is the friction factor, L is the pipe length (m), D is the inside diameter (m), ρ is the density of water (1000 kg/m³ at 4 °C), and V is the velocity (m/s).

Minimum and Maximum Regulatory Pressure

The Canadian Plumbing Code (CPC) requires that the water pressure at every faucet or fixture be at least 150 kPa under conditions of maximum simultaneous flow. The maximum allowable static pressure in a supply system is 550 kPa; beyond this, a pressure-reducing valve must be installed. Pressures exceeding 550 kPa can cause water hammer, leaks at fittings, and premature wear of faucets and valves.

Water Velocity in Pipes

Water velocity in supply pipes must not exceed 2.4 m/s for metallic pipes and 1.8 m/s for plastic pipes, to prevent erosion, noise, and water hammer. For large-diameter pipes (100 mm and larger), a maximum velocity of 3 m/s may be tolerated, but this remains a discouraged practice.

Water Supply Sources

Municipal Water Supply

Connection to the municipal water system is the most common source. The service pipe (entrance line) must be equipped with a main shut-off valve that is accessible, typically located near the building entrance. An additional isolation valve must be installed inside, immediately after the pipe penetrates the building, to allow isolation of the internal system.

A backflow preventer (or backflow prevention device) is mandatory on any potable water supply line connected to a non-potable source or to a fire protection system. The CPC requires backflow protection according to the degree of hazard: high hazard (contamination by toxic substances), moderate hazard (contamination by non-toxic but objectionable substances), or low hazard (no contamination risk).

Private Wells

For a private well, the pump must be sized to provide the maximum simultaneous flow demand of the building. The pressure tank (hydro-pneumatic tank) must maintain a minimum pressure of 150 kPa and a maximum pressure of 550 kPa at the point of use. The pump cut-off pressure is typically set between 280 and 400 kPa, with a differential of 100 to 140 kPa between the start and stop pressures.

Non-Potable Water (Rainwater Harvesting, Greywater)

Systems using non-potable water for irrigation or toilets must be physically separated from the potable water system. Any interconnection is prohibited. Non-potable water pipes must be identified with a distinct colour (purple or labelled), and fixtures must not be interchangeable with those of the potable water supply.

Sizing of Supply Pipes

Plumbing Fixture Unit Method

The CPC defines plumbing fixture units (PFU) for each sanitary fixture. One plumbing fixture unit is equivalent to a flow rate of 0.063 L/s (approximately 1 gpm). The table below presents common values:

The total probable flow rate is determined by adding the plumbing fixture units of all fixtures served by the pipe, then applying a demand curve. The CPC provides conversion tables (Table A-2) that give the probable flow rate based on the total number of plumbing fixture units. For a residential building with fewer than 30 units, the simplified formula may be used:

Q (L/s) = 0.063 × √(Total PFU)

For larger buildings, the CPC demand curve must be used.

Pipe Sizing

The minimum inside diameter is determined based on the probable flow rate and the maximum allowable velocity. The friction head loss is calculated using the Hazen-Williams formula:

ΔP (kPa/m) = 6.05 × 10⁵ × (Q¹·⁸⁵) / (C¹·⁸⁵ × D⁴·⁸⁷)

Where Q is the flow rate in L/min, C is the roughness coefficient (140 for clean copper, 120 for galvanized steel, 150 for CPVC and PEX), and D is the inside diameter in mm.

The total head loss must be subtracted from the static pressure to obtain the available pressure at the last fixture. This available pressure must be at least 150 kPa.

Equivalent Length of Fittings

Each fitting, elbow, tee, or valve adds resistance equivalent to a certain length of straight pipe. The following table gives equivalent lengths in metres for a 25 mm (1 in) pipe:

These values must be multiplied by the correction factor for other diameters (approximately proportional to the diameter).

Piping Materials for Potable Water

Copper Pipes

Copper types M, L, and K are used depending on the working pressure. Type M is the thinnest (working pressure 1100 kPa at 65 °C), type L is intermediate (working pressure 1400 kPa), and type K is the thickest (working pressure 1900 kPa). Fittings are typically soldered with tin (lead-free solder mandatory since 2010) or installed using compression fittings. Copper is corrosion-resistant but may be subject to pitting corrosion if the water pH is below 6.5 or above 8.5.

CPVC Pipes (Chlorinated Polyvinyl Chloride)

CPVC is a thermoplastic that withstands temperatures up to 93 °C and pressures of 1000 kPa. Fittings are joined with a solvent cement specific to CPVC. CPVC is lightweight, easy to install, and corrosion-resistant. It must not be used for hot water above 82 °C on a continuous basis.

PEX Pipes (Cross-linked Polyethylene)

PEX is available in three types: PEX-A (peroxide), PEX-B (silane), and PEX-C (irradiation). PEX-A is the most flexible and most resistant to cracking. PEX is installed with crimp, cinch, or compression fittings. It withstands pressures of 1000 kPa at 82 °C. PEX must not be exposed to direct UV rays for more than 30 cumulative days. PEX pipes are commonly used in residential plumbing for supply systems, with manifolds that distribute water individually to each fixture.

Galvanized Steel Pipes

Galvanized steel is still present in older buildings but is no longer recommended for potable water due to internal corrosion that reduces the effective diameter and releases zinc particles. The CPC permits its use only for large-diameter pipes (75 mm and larger) in commercial buildings.

Material Comparison

Canadian Plumbing Code Rules

Rule 2.6.1.1 — Backflow Protection

Every potable water installation must be protected against backflow by a backflow prevention device conforming to CSA B64 (backflow prevention devices). The choice of device depends on the degree of hazard:

Rule 2.6.2.1 — Hot Water Temperature

Domestic hot water must be maintained at a temperature of at least 60 °C in the storage tank to prevent the growth of Legionella pneumophila bacteria. However, the temperature of water delivered to faucets must not exceed 49 °C in buildings where vulnerable persons (children, elderly) may be exposed. Thermostatic mixing valves must be installed to reduce the temperature to 49 °C at points of use.

Rule 2.6.3.1 — Pipe Insulation

Hot water pipes must be insulated when they pass through unheated spaces or when embedded in a concrete slab. The insulation must have a minimum thickness of 13 mm for pipes smaller than 50 mm in diameter and 25 mm for larger diameters. Insulation reduces heat loss and prevents condensation on cold water pipes.

Rule 2.6.4.1 — Supports and Anchors

Water supply pipes must be supported at maximum intervals depending on the material and diameter:

Rule 2.6.5.1 — Fire Wall Penetrations

Pipes that penetrate a fire wall or floor must be sealed with a certified intumescent product. The seal must maintain the fire separation integrity for at least 45 minutes (F rating).

Water Hammer Protection Systems

Causes and Effects

Water hammer is a transient overpressure caused by the sudden stoppage of flow (rapid closure of a faucet or solenoid valve). The overpressure can reach several times the static pressure and cause noise, leaks, and pipe rupture.

Overpressure Calculation

The maximum overpressure (ΔP) during water hammer is estimated using the Joukowski formula:

ΔP = ρ × a × V

Where a is the pressure wave speed (approximately 1200 m/s for copper, 300 m/s for PEX and CPVC), ρ is the density of water (1000 kg/m³), and V is the initial water velocity (m/s).

For example, for a velocity of 2 m/s in a copper pipe: ΔP = 1000 × 1200 × 2 = 2,400,000 Pa = 2400 kPa. This overpressure is far greater than the working pressure of the pipes, hence the need for water hammer arrestors.

Water Hammer Arrestors

Water hammer arrestors are air chambers or spring-loaded arrestors installed near quick-closing fixtures (dishwasher, washing machine, flush valve toilets). The CPC requires an arrestor when the valve closure time is less than 0.5 seconds. Arrestors must be sized to absorb the volume of water displaced during stoppage.

Pressure Relief and Regulation Systems

Pressure-Reducing Valve

The pressure-reducing valve is installed when the static pressure exceeds 550 kPa. It reduces the pressure to an adjustable value, typically between 300 and 400 kPa. The pressure-reducing valve must be installed with a shut-off valve upstream and downstream, as well as a purge valve to allow maintenance. A check valve must be installed downstream of the pressure-reducing valve to prevent backflow.

Safety Relief Valve

A safety relief valve must be installed on every water heater or pressure tank to relieve excess pressure. The valve must be set at a pressure lower than the maximum working pressure of the tank (typically 1000 kPa for a residential water heater). The discharge from the relief valve must be directed to a drain or outdoors, without any reduction in diameter.

Water Heaters and Hot Water Production

Storage Water Heaters

Storage (tank-type) water heaters are the most common. Their capacity is determined based on the number of occupants and the maximum simultaneous flow rate. The sizing formula is:

Capacity (L) = (Number of occupants × 75 L) / (Recovery factor)

The recovery factor depends on the burner power or heating element rating. For a residential electric water heater, the power is typically 3000 to 4500 W, which gives a recovery factor of approximately 15 to 20 L/h for a ΔT of 50 °C.

Tankless Water Heaters

Tankless water heaters provide hot water on demand. Their maximum flow rate is limited by the available power. For a 27 kW electric tankless heater, the maximum flow rate is approximately 7.5 L/min for a 40 °C temperature rise. For a natural gas tankless heater, the power is typically 150,000 to 200,000 BTU/h (44 to 59 kW), allowing a flow rate of 15 to 20 L/min.

Rule 2.6.6.1 — Thermal Expansion

When water is heated, it expands. In a closed system (with a backflow preventer), this expansion creates a pressure increase. An expansion tank must be installed on the cold water line supplying the water heater. The expansion tank must be sized to absorb the volume increase:

V = (0.0006 × V_tank × ΔT) / (1 - (P_upstream / P_downstream))

Where V_tank is the water heater volume (L), ΔT is the temperature rise (°C), P_upstream is the supply pressure (kPa), and P_downstream is the relief valve set pressure (kPa).

Installation and Commissioning Procedures

Flushing and Disinfection

Before commissioning, all potable water pipes must be flushed with clean water to remove manufacturing and installation debris. Then, disinfection is performed according to the procedure in CSA B483 (drinking water treatment systems): fill the system with a chlorine solution at 50 mg/L, maintain contact for 24 hours, then flush thoroughly until all chlorine is removed.

Pressure Testing

Water supply pipes must undergo a pressure test before being covered or concealed. The test is performed at a pressure of 1.5 times the maximum working pressure, but never less than 1000 kPa, for a duration of 2 hours. The pressure must not drop by more than 35 kPa during the test. Leaks must be repaired and the test repeated.

Pipe Identification

Potable water pipes must be identified with a label or distinct colour. The colour blue is reserved for cold potable water, red for hot water, and purple for non-potable water. Labels must be applied at maximum intervals of 3 metres and at every wall or floor penetration.

Practical Calculations for the Exam

Example 1: Sizing a Main Supply Line

A residential building with 6 dwelling units has the following fixtures per unit: 1 tank-type toilet, 1 lavatory, 1 kitchen sink, 1 bathtub, 1 washing machine. Calculate the probable flow rate.

Step 1: Plumbing fixture units per dwelling unit:

Step 2: Total for 6 dwelling units: 6 × 10.5 = 63 PFU

Step 3: Probable flow rate (simplified formula):

Q = 0.063 × √63 = 0.063 × 7.94 = 0.50 L/s

Step 4: Minimum diameter for a velocity of 2 m/s:

A = Q / V = 0.0005 m³/s / 2 m/s = 0.00025 m²

D = √(4A/π) = √(4 × 0.00025 / 3.1416) = √0.000318 = 0.0178 m = 17.8 mm

The minimum nominal diameter is 20 mm (3/4 in).

Example 2: Verifying Available Pressure

A building has a static pressure of 500 kPa. The 25 mm copper main line has a total length of 30 m (including equivalent lengths). The probable flow rate is 0.5 L/s (30 L/min). Calculate the available pressure at the last fixture.

Step 1: Friction head loss (Hazen-Williams, C = 140):

ΔP = 6.05 × 10⁵ × (30¹·⁸⁵) / (140¹·⁸⁵ × 25⁴·⁸⁷)

First, calculate the powers:

30¹·⁸⁵ ≈ 30 × 30⁰·⁸⁵ ≈ 30 × 18.5 ≈ 555

140¹·⁸⁵ ≈ 140 × 140⁰·⁸⁵ ≈ 140 × 63.5 ≈ 8890

25⁴·⁸⁷ ≈ 25⁴ × 25⁰·⁸⁷ ≈ 390,625 × 16.2 ≈ 6,328,125

ΔP = 6.05 × 10⁵ × 555 / (8890 × 6,328,125) = 335,775,000 / 56,257,031,250 ≈ 0.006 kPa/m

Step 2: Total head loss:

ΔP_total = 0.006 × 30 = 0.18 kPa

Step 3: Available pressure:

P_available = 500 - 0.18 = 499.82 kPa

The available pressure is well above 150 kPa, so the sizing is acceptable.

Example 3: Sizing a Pressure-Reducing Valve

A building has a static pressure of 700 kPa. The maximum simultaneous flow rate is 1.2 L/s. Determine the required pressure-reducing valve.

The pressure-reducing valve must reduce the pressure from 700 kPa to 400 kPa. The flow rate of 1.2 L/s (72 L/min) requires a 25 mm (1 in) pressure-reducing valve with a flow coefficient (Cv) of at least:

Cv = Q / √(ΔP) = 72 / √(300) = 72 / 17.32 = 4.16

A 25 mm pressure-reducing valve with a Cv of 5 is sufficient.

Common Pitfalls to Avoid

Summary

Master these concepts, redo the example calculations without looking at the solutions, and you will be well prepared for the Red Seal exam questions on water supply systems.