Cold Water Storage and Backflow
Cold Water Basics · Plumbing
Some homes feed their taps straight from the mains, while others store water in a cistern first. This topic explains direct and indirect systems, float valves and why backflow protection matters.
In a direct system most cold taps are fed from the mains. In an indirect system many outlets draw from a storage cistern, usually in the loft, which a float valve refills and then shuts off as the water level rises.
Backflow is water flowing the wrong way, from an appliance, a hose or a cistern back towards the supply. Water is graded into fluid categories by the harm it could do, and the higher the risk, the stronger the protection needed between it and drinking water, up to a physical air gap.
Some water fittings work needs notice to, and consent from, the water supplier before it starts. The lessons show how to recognise when that may apply, and the rules differ between England, Wales, Scotland and Northern Ireland.
Contamination risk decides the protection
Updated
How to reason about the system
Backflow can result from a pressure drop upstream or higher pressure downstream. An arrangement suitable for one fluid category may be unsuitable for another. Water Regs UK explains the differences between backflow devices and air-gap arrangements; the water supplier can advise on the applicable case.
Questions to take further
- Is a double check valve suitable for every backflow risk?
- No. Protection must match the fluid category and the pressure conditions. Higher-risk uses can need an appropriate air gap or other suitable arrangement; do not choose a device merely because it fits the pipe.
Sources
- Water Regs UK: backflow protection — Contamination risks and why protection must match the fluid category and conditions.
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Lessons on the plumbing path
- Direct and indirect systems
- Cisterns and float valves
- Backflow and why it matters
- Notifying the water supplier
Terms to know
Before you start: some plumbing work is regulated or notifiable
Some water fittings work needs notice to, and consent from, the water supplier before it starts. Check the rules where you live.
Gas work is for competent workers covered by a Gas Safe registered business in Great Britain. Northern Ireland has separate gas regulations. Do not work on gas pipes or appliances yourself.
In England, installing an unvented hot-water system over 15 litres is notifiable building work: use a competent installer registered with a competent-person scheme, or tell building control before work starts. Leave this work to a suitably skilled person.
Wales, Scotland and Northern Ireland have their own water and building rules; check which apply before work starts. Electrical connections belong with an electrician.
This guide does not qualify you or make you competent, approved or registered for plumbing, gas or unvented work.