Installing a water supply system correctly means more than joining pipe: it means routing and supporting pipework properly, isolating sections safely, avoiding cross connections that could contaminate potable water, and proving the finished system holds pressure before it is handed over. This guide covers water supply layout and routing, valve and isolation practice, backflow prevention, the pressure-testing procedure, and flushing and commissioning before a system is put into service.
Saudi Skill Test is an independent preparation resource and is not affiliated with the Saudi government, Takamol or NSDC. This guide does not reproduce or claim knowledge of official exam questions; it is a study aid built from public technical standards and general trade practice.
Understanding Water Supply Layout
A water supply system typically runs from a main or storage source through a distribution network to individual fixtures, and understanding this layout before work begins prevents costly rework. A plumber should be able to trace the supply from its point of entry, through the main isolation valve, branch lines, and any pressure-reducing or backflow-prevention devices, to each fixture. Cold- and hot-water lines are generally run separately, with hot-water branches sized and insulated per the project design, and the two are never cross-connected except through an approved mixing device.
Understanding the layout also means recognising the difference between a direct system, where fixtures are fed straight from the incoming main or a booster pump, and an indirect or storage-fed system, where a break tank or storage vessel supplies part of the building at a lower, controlled pressure. The two arrangements have different isolation, backflow, and pressure-testing implications, and a plumber should confirm which arrangement is in use from the project drawings before assuming how a given branch behaves.
Reading the Work Area
Before routing pipe, a plumber should identify structural elements to avoid (load-bearing walls, slabs, existing services), other trades' work in the same space (electrical conduit, HVAC ductwork), and any as-built drawings or service routes already installed. Marking planned pipe routes and fixture positions before cutting or drilling reduces clashes with other services and avoids the need to relocate completed work.
Safety Warning: Before drilling, chasing, or cutting into any wall, floor, or ceiling, confirm the location of existing electrical cabling and gas or other service lines using the appropriate detection method for the site. Striking a live electrical cable or a gas line with a drill or saw is a serious injury and fire risk.
Pipe Routing and Supports
Pipe should be routed to avoid unnecessary bends, kept accessible for future maintenance where practical, and protected from mechanical damage, direct sunlight (for plastic pipe), and extremes of temperature. Horizontal and vertical runs must be supported at intervals that prevent sagging, noise from thermal movement, and stress on joints; the correct support spacing for a given pipe material, diameter, and orientation is a design and code value, not a figure to be judged by eye, and must be taken from SBC 701, the project drawings, or the pipe manufacturer's installation guide. Pipe passing through structural elements should use sleeves where specified, allowing for thermal expansion and preventing the pipe from bearing directly on masonry or concrete.
Where a pipe run changes direction, crosses an expansion joint in the building structure, or connects to a fixed point such as a wall-mounted appliance, an allowance for thermal movement (an expansion loop, a flexible section, or a sliding support, depending on the material and manufacturer's guidance) should be included, since a rigidly restrained plastic or metal pipe run can develop stress at the joints as it heats and cools through normal use. Support hangers and clips should be sized for the pipe's outside diameter and insulation thickness where insulated, and should not be over-tightened to the point of deforming plastic pipe.
Valves and Isolation
Every water supply installation needs isolation points that allow sections to be shut down for maintenance without draining the whole system. A main isolation valve should be installed at the point of entry, and branch isolation valves at each fixture group or major branch, so that a repair to one fixture does not require shutting off supply to the entire building. Valves should be installed in accessible locations, correctly oriented per the manufacturer's markings, and labelled where the system is complex enough that isolation points are not otherwise obvious.
Connecting Fixtures
Fixture connections should use the correct isolation valve, supply pipe size, and fitting type specified for that fixture, with flexible connectors used only where the manufacturer or project specification permits them. Every fixture connection should be independently isolable so a single tap, toilet, or appliance can be serviced without shutting down the branch it sits on. Manufacturer instructions for a specific fixture (a mixer, a water heater, an appliance supply) take precedence over generic practice where they differ, since fixture connection requirements vary between products.
Water heaters and other pressurised appliances often have their own specific connection requirements, such as a dedicated pressure-relief or expansion device, that are separate from the general water-supply isolation valve. These requirements should be read from the appliance's own installation manual rather than assumed to match a standard fixture connection, since omitting a required safety device on a pressurised appliance is a defect that may not become apparent until the appliance is in service.
Avoiding Cross Connections
A cross connection is any point where a potable water line could become connected, directly or indirectly, to a non-potable source — for example a hose submerged in a bucket, an irrigation system, or a boiler feed. BS EN 1717:2025+A1:2026 sets out the general principles and device categories used to protect potable water installations against pollution by backflow, and an appropriate backflow-prevention device (such as a check valve, vacuum breaker, or air gap, selected per the applicable standard and the specific hazard category of the connected fixture) must be installed at every point of risk. Materials and fittings used in potable-water contact — pipe, valves, gaskets, and jointing compounds — should be confirmed against NSF/ANSI 61 or an equivalent recognised potable-water certification, since not every plumbing product is rated for drinking-water contact.
Backflow can occur by two distinct mechanisms: backpressure, where downstream pressure exceeds the supply pressure and pushes water back up the line, and backsiphonage, where a drop in supply pressure creates a vacuum that draws water (and any contaminant it is in contact with) back into the potable system. The correct backflow-prevention device depends on which mechanism is credible at a given connection and on the hazard level of the connected fluid, and this selection should follow EN 1717's device categories or the applicable Saudi code requirement rather than a single device being used everywhere by default.
Safety Warning: Never connect a potable water supply directly to an irrigation system, chemical dosing unit, or any non-potable source without an approved backflow-prevention device rated for that specific hazard level. An uncontrolled cross connection can draw contaminated water back into the drinking-water supply.
Pressure Testing
Every new or modified water supply installation must be pressure tested before it is concealed or put into service, to confirm there are no leaks and that all joints hold under the system's working conditions.
Preparation
Confirm all joints are complete, inspected, and (for solvent-cement or fusion joints) fully cured per the manufacturer's stated time before applying test pressure. Confirm open ends are correctly capped or plugged, and that any components not rated for the test pressure (certain fixtures, gauges, or temporary equipment) are removed or isolated from the section under test.
Isolation
Isolate the section being tested from the rest of the system and from any live supply, so the test pressure is applied only to the section intended and cannot pressurise sections not yet ready for test or unrelated parts of the building.
Pressurization
Pressurize the system using the test medium, pressure, and duration specified in SBC 701, the project's technical specification, or the manufacturer's commissioning instructions for the pipe material used — this guide does not state a test pressure or duration from memory, since the correct figure depends on the pipe material, system design pressure, and applicable code clause, and must always be confirmed from one of those sources before testing.
Inspection
With the system holding pressure, inspect every joint, fitting, and valve visually for weeping, dripping, or pressure drop, and check the test gauge for any fall in pressure over the specified hold period, which would indicate a leak even where none is visible.
Documentation
Record the test date, section tested, test medium, pressure applied, hold duration, and result (pass/fail with any remedial action) on a test record, since an undocumented pressure test is not verifiable at handover or during a later inspection.
Safety Warning: Never loosen, disconnect, or attempt to repair a fitting, valve, or joint while the system is still pressurised. Fully depressurise and isolate the section first — a fitting that separates under pressure can eject with enough force to cause serious injury.
Flushing and Commissioning
After a successful pressure test, the system should be flushed to clear debris, cutting residue, flux, or jointing compound before it is placed into service, using a flow rate and duration appropriate to the pipe size and system volume as specified in the project commissioning procedure or manufacturer guidance. Where the system supplies potable water, flushing and any required disinfection should follow the applicable code or water-authority requirement rather than a generalised assumption, since disinfection procedures and contact times are specified figures, not estimates.
Installation Defects
- Pipe supported at intervals wider than the material manufacturer or code allows, leading to sagging and joint stress over time.
- A backflow-prevention device omitted or of the wrong hazard category at a cross-connection risk point.
- Isolation valves omitted at fixture level, forcing a full building shutdown for a minor repair.
- A section pressure tested before all joints in that section were complete or fully cured.
- Flushing skipped or rushed, leaving debris in the system that later blocks strainers, valves, or fixture aerators.
- Test results not documented, leaving no record to confirm the installation was verified before concealment.
Sample Pressure-Test Record
| Field | Entry |
|---|---|
| Section tested | Cold-water branch, first-floor bathroom |
| Test medium | Water (per project specification) |
| Test pressure | As specified in SBC 701 / project spec — see manufacturer/code reference |
| Hold duration | As specified in SBC 701 / project spec |
| Start/end gauge reading | Recorded at test time |
| Result | Pass / Fail (with remedial action if failed) |
| Tested by / date | Technician name and date |
Valve Identification Table
| Valve Type | Typical Location | Function | Key Feature |
|---|---|---|---|
| Gate valve | Main isolation, branch isolation | Full open/close isolation | Not intended for throttling flow |
| Ball valve | Fixture isolation, branch shutoff | Quarter-turn open/close | Fast operation, clear open/closed indication |
| Check valve | Backflow-risk points, pump discharge | Allows flow in one direction only | Prevents reverse flow/backflow |
| Pressure-reducing valve | Building or branch inlet | Reduces incoming pressure to a set range | Set per manufacturer/project spec, not by eye |
| Vacuum breaker | Hose bibs, irrigation connections | Prevents backsiphonage | Required at specific cross-connection risk points |
Handover Checklist
- All joints visually inspected and confirmed complete before testing
- Section correctly isolated from live supply before pressurization
- Test pressure and duration taken from code, spec, or manufacturer source (not memory)
- No visible leaks or pressure drop observed during the hold period
- Backflow-prevention devices installed at every identified cross-connection risk
- Pipe supports installed at the spacing specified for the material and diameter
- System flushed before commissioning
- Pressure-test record completed and retained
- Isolation valves confirmed accessible and correctly labelled
A Worked Example
A plumber completes a new cold-water branch feeding two bathrooms using a mix of solvent-cement and compression joints. The solvent-cement joints are confirmed to have passed their manufacturer-stated cure time before proceeding; the compression joints, which do not have a curing stage, are instead visually inspected and confirmed tightened to the manufacturer's specified point. The branch is isolated from the rest of the building's live supply using the nearest upstream valve, and open ends are capped. The plumber checks the project specification for the required test pressure and hold duration for this pipe material and finds both values listed against the applicable SBC 701 clause; no figure is assumed. The section is pressurized to that value using a calibrated test pump and gauge, and held for the specified duration while every joint is visually inspected for weeping and the gauge is watched for any drop. No leak or pressure loss is observed, so the result is recorded as a pass on the test record, with the pressure, duration, and source clause noted. The branch is then flushed at the flow rate given in the commissioning procedure before the isolation valve is opened to bring the new branch into service. Every specific figure in this example — support spacing, test pressure, hold time, and flush rate — came from the project specification or SBC 701, never from memory.
Internal Links
- Plumber profession page
- Plumber practice tests
- P1: Plumber Tools, Pipes and Jointing Methods
- P3: Drainage, Traps and Venting
- P4: Plumbing Fault-Finding and Troubleshooting
- P5: Plumber Safety and Practical Work Readiness
References
- Saudi Building Code National Committee. SBC 701: The Saudi Plumbing Code, 2024 edition. sbc.gov.sa
- BSI Group. BS EN 1717:2025+A1:2026 — Protection Against Pollution of Water Intended for Human Consumption in Potable Water Installations and General Requirements for Devices to Prevent Pollution by Backflow. knowledge.bsigroup.com
- NSF International. NSF/ANSI/CAN 61: Drinking Water System Components — Health Effects. nsf.org
- ASTM. ASTM B88: Seamless Copper Water Tube. store.astm.org
- International Organization for Standardization. ISO 15874-1:2013: Plastics Piping Systems for Hot and Cold Water Installations — Polypropylene (PP) — Part 1: General. iso.org
Note on scope: This guide does not state pipe-support spacing, pressure-test values, hold durations, or flushing flow rates as fixed numbers, since these depend on pipe material, diameter, system design, and the applicable code clause. Always take the exact figure from SBC 701, the project specification, or the pipe/fitting manufacturer's documentation.