Image by Water Regs UK Ltd
Cold water storage cisterns play a critical role in maintaining safe, reliable water supply within buildings. Whether serving domestic, commercial, or industrial systems, their design must prioritise water quality, durability, and compliance with current regulations and standards.
This article outlines the key design requirements and best practice considerations for cold water storage cisterns.
Material Standards and Suitability
All components used in the construction and operation of a cold-water storage cistern must be of appropriate quality and fit for purpose.
Materials must be:
- Durable and resistant to corrosion or degradation
- Suitable for long-term contact with potable water
- Designed to maintain structural integrity over the life of the installation
Compliance with BS 6920
All non-metallic materials in contact with water, including internal surfaces and areas where condensation may form, must comply with the current version of BS 6920 (or an equivalent standard).This ensures that materials:
- Do not leach harmful substances into the water
- Do not affect the taste, odour, or appearance of the water
- Are safe for use in potable water systems
Watertight Construction
Cisterns must be fully watertight, preventing leakage and protecting against contamination ingress.
Where required, tanks should be:
- Internally lined or coated with impermeable, WRAS-approved materials
- Constructed to withstand operational pressures and environmental conditions
Proper sealing at joints, connections, and penetrations is essential to maintain system integrity.
Essential Components and Connections
A compliant cold water storage cistern must include the following key features:
Inlet and Float Valve Arrangement
Controls the incoming water supply and maintains the correct water level.
Outlet Connection
Positioned to minimise the risk of drawing off settled debris.
Overflow and Warning Pipe
Provides a visible and safe discharge route in the event of overfilling, helping to prevent property damage and identify faults quickly.
Screened Ventilation
Allows air movement while preventing the ingress of insects, debris, and contaminants.
Covers and Protection Against Contamination
Every cistern must be fitted with a rigid, close-fitting, and securely fixed lid or cover.This is essential to:
- Prevent the ingress of dust, insects, vermin, and debris
- Reduce the risk of contamination
- Limit light penetration, which can encourage biological growth
Cisterns and lids should be constructed from materials that:
- Do not shatter or fragment if damaged
- Are robust enough to withstand operational and environmental stresses
Additional Best Practice Considerations
While not always explicitly stated, best practice design should also include:
Access for Inspection and Maintenance
Cisterns should be designed with appropriate access points to allow for routine inspection, cleaning, and maintenance in line with HSE guidance.
Prevention of Stagnation
Designs should minimise areas where water can stagnate by:
- Ensuring correct sizing relative to demand
- Avoiding dead legs or poorly circulated zones
Thermal Protection
Where installed in areas subject to temperature variation, insulation should be provided to:
- Prevent freezing
- Limit heat gain, reducing the risk of bacterial growth
Backflow Protection
Appropriate air gaps (e.g. Type AB where required) must be incorporated in accordance with the Water Supply (Water Fittings) Regulations 1999 to prevent contamination of the mains supply.
Structural Support and Installation
Cisterns must be adequately supported and installed on suitable bases to prevent deformation, stress, or long-term structural issues.
Compliance and Responsibility
Ensuring that a cold-water storage cistern meets these design requirements is essential for:
- Protecting public health
- Maintaining water quality
- Meeting regulatory and legal obligations
- Supporting long-term system performance
Working with experienced, competent manufacturers and suppliers, such as members of the ATCM, helps ensure that cisterns are designed, manufactured, and installed to the highest standards.
Conclusion
Cold water storage cistern design is about more than just containment, it is about safeguarding water quality, ensuring compliance, and delivering reliable performance over time. By adhering to recognised standards such as BS 6920 and following best practice design principles, duty holders can ensure their systems remain safe, efficient, and fit for purpose.
