Most water emergencies give you warning. A storm forecast, a burst main up the road, a boil notice, a hard freeze coming. The gap between knowing and losing supply is usually somewhere between ten minutes and a day.
What you do in that window matters more than almost anything else in this domain, because water already in the house needs no filtering, no fuel and no work.
The ten minute window
The moment you have reason to think the supply is at risk, before anything else:
Fill drinking containers first, always. Clean sealed bottles of mains water are the highest-value water in the house and stay good for months. The bath is the largest volume and the lowest quality; do it while the bottles are filling.
Run the cold tap, not the hot, for anything you intend to drink. Hot water has been sitting in a cylinder, may be from a header tank rather than the main, and is not intended as drinking water.
A bath is not a drinking water store
This is the part that gets glossed over in most preparedness advice.
If a bathful is genuinely all you have and someone must drink it, filter it and then boil it, and accept that it may still taste of soap.
The liner, which changes everything
A bath water storage liner, sold as a WaterBOB or similar, is a large food-grade plastic bag that sits in the bath, fills from the tap through a supplied hose, and seals. It typically holds 250 to 300 litres.
It costs very little, packs down to the size of a paperback, and it converts your largest container from washing water into genuine drinking water. For the money, it is one of the highest-value preparedness items in the house.
Using one:
- Rinse the bath first. The liner will be in contact with it.
- Lay the liner in flat, opening upward, and unfold it fully before adding water. A liner that fills with a fold in it holds much less and can split at the crease.
- Fill from the cold tap using the supplied hose adaptor. It takes 20 to 30 minutes.
- Seal it properly. The cap and the fill point are the only places contamination gets in.
- Draw water with the supplied pump, not by opening the top. Every opening lets air, dust and hands in.
- Do not sit or lean on it. They are tough but not indestructible, and 300 litres is a great deal of water to lose across a bathroom floor.
How long the water keeps. Sealed, from a clean mains supply, in a food-grade liner, kept dark and cool: several weeks to a few months is realistic. Water does not spoil on its own; what changes is whatever got in with it and whatever grows from that. The bathroom is warmer than ideal, so the honest answer is to use it inside a few weeks rather than treat it as long-term storage. Rotate it if the emergency does not arrive.
Everything else you can fill
Once the bath is filling, keep going. Volume matters more than elegance.
- Every saucepan, bowl, jug and kettle. Lid on or cling film over.
- Buckets, then a plate on top to keep dust and insects out.
- The washing machine drum, which holds a surprising amount and is right next to nothing useful, but it flushes a toilet.
- Bin bags inside a bin. Doubled up, inside a clean bin, this holds a lot. Not drinking water, but perfectly good for flushing.
- The water butt, if the forecast includes rain. See the rainwater system page.
- Hot water bottles, camping containers, the caravan tank, the paddling pool.
Anything holding water is worth filling. You can always tip it away.
Water already in the house
Before the mains was cut, water was already sitting in your building. Most people never think of it.
- The hot water cylinder. Typically 100 to 200 litres, and it is mains-quality water. There is a drain cock at the bottom. Turn off the immersion heater or boiler first, or you will burn out the element heating an empty cylinder. Let it cool before drawing it off. This is the largest single hidden store in most houses.
- The cold water tank in the loft, on older systems. Often 200 litres or more. Quality varies: it is open to the loft, so check for debris, insects and rodent access before trusting it. Filter and boil it. On a modern combi system there is no tank.
- The pipework itself. Open the lowest tap in the house, usually a downstairs cold tap or an outside tap, and open a tap upstairs to let air in. The pipes will drain by gravity into whatever you put underneath.
- Toilet cisterns, not the bowls. Clean water, though if there is a blue block or a cleaning cartridge in the cistern it is not drinkable. Perfectly good for flushing, which is what it was already for.
- The central heating system. Not drinkable under any circumstances. It contains corrosion inhibitor and it has been sitting in radiators. Useful only for flushing, and even then it stains.
Do this early, before pressure drops completely, because once the mains is off and the system has drained the water in the pipes has already gone.
Managing the store
Label everything. Masking tape and a marker: DRINK, WASH, FLUSH. In the third day of an emergency, in poor light, with people tired, nobody remembers which bucket was which, and one wrong guess undoes the whole system.
Keep them apart physically. Drinking containers in one room, washing water in another if you can. Separation by habit beats separation by memory.
Use the worst water first, provided it is suitable for the job. Open buckets go first because they are deteriorating fastest; sealed bottles keep and should be the reserve.
Cover everything. An open container collects dust, insects and whatever is in the air, and in a hot room it grows things. A plate, cling film or a lid costs nothing.
Date what you seal. A marker line on the bottle with the date you filled it turns a guess into a fact three weeks later.
Ration from the first day, not the day you notice it running low. The playbook's water chapter has the daily figures. Working out on day four that you should have been rationing since day one is the classic and entirely avoidable failure, and it is much easier to relax a ration than to impose one late.