# Water Supply Systems Water supply systems deliver potable water from the municipal main or private source to every fixture, appliance, and process point within a building. The architect must understand pipe routing, riser locations, plant room requirements, storage tank sizing, and the coordination of water services with structural and architectural elements. Reliable water supply is fundamental to building function, and its infrastructure significantly impacts vertical risers, ceiling voids, and plant room allocation. --- ## Table of Contents - [Supply Fundamentals](#supply-fundamentals) - [System Types](#system-types) - [Pipe Sizing Principles](#pipe-sizing-principles) - [Pipe Materials](#pipe-materials) - [Pumping Systems](#pumping-systems) - [Storage and Tanks](#storage-and-tanks) - [Hot Water Systems](#hot-water-systems) - [Backflow Prevention](#backflow-prevention) - [See Also](#see-also) --- ## Supply Fundamentals | Term | Description | |------|-------------| | **Mains pressure** | Pressure from municipal supply (typically 2–5 bar in UK) | | **Static head** | Pressure from height of water column (1 bar ≈ 10.2m head) | | **Flow rate** | Volume of water per unit time (L/s or L/min) | | **Demand** | Peak simultaneous flow requirement | | **Diversity** | Statistical reduction factor — not all fixtures used simultaneously | | **Loading units** | Numerical values assigned to fixtures for demand calculation | | **Residual pressure** | Pressure remaining at fixture after friction losses | --- ## System Types | System | Description | Application | |--------|-------------|-------------| | **Direct (unvented)** | Fixtures fed directly from mains pressure | Low-rise buildings where mains pressure is adequate | | **Indirect (vented)** | Cold water storage cistern at high level; gravity-fed | Traditional UK system; hospitals (resilience) | | **Boosted** | Pumps increase pressure for upper floors | Buildings exceeding mains pressure capability | | **Break tank + booster** | Mains fills break tank; pumps distribute | High-rise buildings; isolates building from mains fluctuation | | **Pressure-reducing valves** | Reduces mains pressure to zones | Tall buildings with high base pressure | ### High-Rise Zoning | Zone | Floors (typical) | Supply Method | |------|-------------------|---------------| | Low zone | Ground – 8 | Direct mains or low-pressure booster | | Mid zone | 9 – 20 | Intermediate booster set | | High zone | 21 – 35 | High-pressure booster set | | Sky zone | 35+ | Dedicated booster with break tanks | Maximum static pressure at any fixture: typically 6 bar (to prevent noise, wear, water waste). Pressure-reducing valves installed at zone boundaries. --- ## Pipe Sizing Principles | Factor | Influence | |--------|-----------| | **Design flow rate** | Determined from fixture loading units and diversity | | **Velocity limit** | 1.5–2.0 m/s for mains; 1.0–1.5 m/s for branches (noise control) | | **Pressure available** | Mains pressure minus static head minus friction losses | | **Friction losses** | Depend on pipe material, diameter, flow rate, fittings | | **Dead legs** | Minimise distance from hot water source to fixture (<3m recommended) | ### Fixture Loading Units (BS EN 806) | Fixture | Cold LU | Hot LU | |---------|---------|--------| | WC cistern | 2 | — | | Wash basin | 1.5 | 1.5 | | Bath | 10 | 10 | | Shower | 3 | 3 | | Kitchen sink | 3 | 3 | | Dishwasher | 3 | — | | Washing machine | 3 | 3 | --- ## Pipe Materials | Material | Application | Advantages | Limitations | |----------|-------------|------------|-------------| | **Copper** | Traditional; all applications | Proven, recyclable, bacteriostatic | Cost, skilled labour for soldering | | **MLCP (Multilayer)** | Press-fit system | Fast installation, flexible, corrosion-free | Fittings cost, thermal expansion | | **PPR (Polypropylene)** | Hot and cold supply | Chemical resistant, fusion welded | Larger diameter, thermal expansion | | **PEX (Cross-linked PE)** | Hot and cold supply | Flexible, freeze-resistant | UV-sensitive, diffusion risk | | **Stainless steel** | High-quality, healthcare | Durable, hygienic | High cost | | **MDPE** | Underground mains | Flexible, corrosion-free | Not for hot water | --- ## Pumping Systems | System | Description | |--------|-------------| | **Single booster set** | Duty + standby pumps; variable speed drives | | **Twin booster set** | Duty/assist/standby for larger buildings | | **Packaged booster** | Factory-assembled unit with pumps, controller, pressure vessel | | **Pressurisation unit** | Maintains system pressure in sealed systems | ### Design Considerations | Factor | Requirement | |--------|-------------| | Noise | Anti-vibration mounts; flexible connections; locate away from bedrooms | | Redundancy | Duty/standby minimum; N+1 for critical buildings | | Energy | Variable speed drives to match demand | | Space | Allow 1.5× pump footprint for maintenance access | | Controls | BMS integration; pressure/flow monitoring; alarm | --- ## Storage and Tanks | Storage Type | Application | |-------------|-------------| | **Break tank** | Isolates building supply from mains; booster pump suction | | **Header tank** | Gravity supply to lower fixtures (indirect system) | | **Hot water cylinder** | Stores heated water for distribution | | **Calorifier** | Indirect cylinder heated by LTHW or steam | | **Buffer vessel** | Absorbs demand peaks; reduces pump cycling | ### Sizing | Building Type | Cold Storage Allowance | |---------------|----------------------| | Office | 45 L/person/day | | Hotel | 150–200 L/room/day | | Hospital | 350–450 L/bed/day | | Residential | 120–150 L/person/day | | School | 30–45 L/pupil/day | Storage duration typically 4–8 hours of average demand; more for critical buildings (hospitals: 24 hours). --- ## Hot Water Systems | System | Description | Application | |--------|-------------|-------------| | **Centralised storage** | Calorifier/cylinder stores hot water | Hotels, hospitals, residential blocks | | **Instantaneous** | Plate heat exchanger or combi boiler; no storage | Offices, small buildings, point-of-use | | **Semi-instantaneous** | Small storage + heat exchanger for peak shaving | Medium commercial | | **Solar thermal** | Solar collectors preheat water; supplemented by boiler | All building types; maximise with south-facing roof | | **Heat pump** | Air or ground source heat pump heating water | Low-carbon alternative to gas | ### Legionella Prevention | Measure | Requirement | |---------|-------------| | Storage temperature | ≥60°C in calorifier | | Distribution temperature | ≥55°C at all points (return ≥50°C) | | Dead legs | Minimise; maximum 3m from circulation loop | | Circulation pump | Continuous or timed; maintain temperature | | Monthly flush | Infrequently used outlets flushed weekly | | Risk assessment | L8/HSG274 compliance (UK); annual review | --- ## Backflow Prevention | Device | Application | |--------|-------------| | **Air gap (AA/AB)** | Highest protection; physical break between supply and receiving vessel | | **RPZ valve** | Reduced Pressure Zone; commercial/industrial cross-connection protection | | **Double check valve** | Standard commercial protection | | **Single check valve** | Low-risk domestic applications | Backflow protection required wherever potable supply could be contaminated by non-potable sources (cooling systems, irrigation, process water). --- ## See Also - [[Sanitary Drainage Design]] - [[Hot Water Systems]] - [[Rainwater Harvesting Systems]] - [[HVAC Fundamentals]] - [[Plumbing and Water Supply Systems]] - [[Fire Safety Building Regulations]] --- #water-supply #plumbing #pipe-sizing #hot-water #legionella #pumping #building-services