給水設備とは — What Are Building Water Supply Systems?
A building's water supply system delivers safe, adequate water at the right pressure to every point of use — from kitchen taps and showers to fire suppression systems and cooling towers. In Japan, the design and installation of water supply systems are governed by the 水道法 (Waterworks Act) and local municipal waterworks regulations, making compliance a non-negotiable starting point for any project.
主な給水方式の比較 — Comparing the Three Main Supply Methods
1. 直結直圧方式 (Direct Pressure / Direct Connection)
Water is supplied directly from the municipal main to each fixture without intermediate storage. This is the simplest and most hygienic method because water never sits in a storage tank where bacteria can proliferate.
- 適用範囲: Low-rise buildings (typically up to 3–4 storeys) where municipal pressure is sufficient
- メリット: No tank maintenance, lower installation cost, freshest water quality
- デメリット: Dependent on municipal pressure; may fail during supply disruptions
2. 受水槽方式 (Storage Tank System)
Water from the municipal main fills a ground-level storage tank (受水槽), which then feeds a rooftop tank (高置水槽) via a pump, supplying fixtures by gravity. This was the dominant method for medium and high-rise buildings for decades.
- 適用範囲: Mid-rise and high-rise buildings; facilities requiring large reserve capacity (hospitals, hotels)
- メリット: Provides a water reserve during supply interruptions; stable pressure by gravity
- デメリット: Tanks require regular cleaning (法定点検) and are a potential contamination risk; higher maintenance cost
3. 直結増圧方式 (Booster Pump Direct Connection)
A pressure booster pump (増圧ポンプ) installed inline amplifies municipal water pressure to serve upper floors without an intermediate storage tank. This method has become the preferred choice for new mid-rise residential buildings in Japan since municipalities began permitting it more widely.
- 適用範囲: Mid-rise residential buildings (typically up to 10–15 storeys depending on municipality)
- メリット: No rooftop tank, better water freshness than tank systems, compact equipment
- デメリット: Pump failure can cut supply to all floors; requires reliable power
給水方式の選定フロー — Selection Flow
- Confirm the available municipal pressure at the service connection (給水圧力の確認).
- Determine the building height and number of supply floors.
- Calculate daily and peak water demand using SHASE (空気調和・衛生工学会) design guidelines.
- Check with the local waterworks authority whether direct booster connection is permitted.
- Evaluate water quality requirements — facilities such as hospitals may mandate tank systems for reserve capacity.
- Compare lifecycle costs including installation, energy (pump operation), and maintenance.
衛生管理の重要ポイント — Key Hygiene Management Points
Water quality in building plumbing systems is directly regulated under the 建築物における衛生的環境の確保に関する法律 (Building Sanitation Act), which applies to buildings over 3,000㎡ used for offices, commercial, or similar purposes. Key obligations include:
- Storage tanks must be inspected and cleaned at least once per year by a registered sanitation manager.
- Water quality tests (残留塩素, 濁度, pH, etc.) must be conducted at prescribed intervals.
- Records of all inspections and test results must be retained for three years.
- Legionella risk assessment is mandatory for buildings with cooling towers, hot tubs, or humidification systems connected to the water system.
配管材料の選択 — Choosing Pipe Materials
| 材料 (Material) | 特徴 (Characteristics) | 主な用途 (Common Use) |
|---|---|---|
| 架橋ポリエチレン管 (PEX) | Flexible, corrosion-free, easy installation | Residential supply, hot/cold |
| ポリブテン管 (PB) | Excellent heat resistance, lightweight | Hot water distribution |
| 塩化ビニル管 (PVC/HIVP) | Low cost, corrosion-resistant | Cold water, drainage |
| ステンレス鋼管 | Long service life, hygienic | Hospitals, food processing |
まとめ
Choosing the appropriate water supply method and pipe materials for your building requires balancing pressure availability, height, water quality standards, and lifecycle cost. Early coordination with the local waterworks authority and a licensed 管工事士 (piping works engineer) will ensure a compliant, efficient, and hygienic water supply system from day one.