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✅ HelpfulWater Supply & Storage
The Cold Water Storage Tank
Not all homes have one — but if yours is older, there may be a large tank in the loft feeding your bathroom cold supplies.
🔍 What it is
Usually a rectangular black, blue, or grey plastic tank in the loft on a platform. It refills from the mains via a ball valve and should have a lid, insulation, and an overflow pipe to the outside.
⚠️ Signs of a problem
Water dripping from an overflow pipe at loft level — the ball valve isn't shutting off. No cold water to bathroom taps while the kitchen still works — the ball valve may be stuck. A green or brown tinge to bathroom tap water — the tank may need cleaning.
🛠 What to tell an engineer
"I have a cold water storage tank in the loft — the overflow outside is dripping and I think the ball valve might need replacing." A plumber can fix this quickly.
Worth knowing: Cold water tanks should be inspected and cleaned every few years, especially in older properties. Contaminated stored water can be a health concern.
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General guidance only — not a substitute for professional advice. Always consult a qualified engineer if you are unsure. Gas work must only be carried out by a Gas Safe registered engineer. Unvented (pressurised) hot water systems must be worked on by a G3-qualified engineer. We accept no liability for any loss, damage, or injury arising from the use of this information.
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The Hot Water Cylinder