Let me give you the main point first, no fuss.
Plan for 3 litres of water per person per day
, at least 3 days (72 hours). For a family of four that comes to 36 litres. Two litres of that is for drinking, one litre for cooking and a bit of hygiene.
That’s the official advice from the government and the water companies. Nothing more.
And no, you don’t need to get nervous about this. A burst pipe, a power cut at the pumping station or a brief contamination of the mains: it rarely happens, but it does happen. When it does, a few jerrycans in the cupboard are simply nice to have.
Don’t panic, do be prepared. In this article you’ll read exactly how much you need, what to store it in, how long it keeps and how to get water clean when your supply runs out.
How much water do you need for an emergency?
The maths is simple: 3 litres per person per day.
The split works like this:
- 2 litres for drinking (your body really needs it, especially when it’s warm)
- 1 litre for cooking and minimal hygiene (brushing teeth, hands)
The official guidance uses 72 hours as a minimum. That’s usually how long it takes before emergency supplies arrive, for example an emergency water point nearby or a tanker.
Here’s how many litres you should store, at a glance:
| Number of people | 3 days (minimum) | 7 days (comfortable) |
|---|---|---|
| 1 person | 9 litres | 21 litres |
| 2 people | 18 litres | 42 litres |
| 3 people | 27 litres | 63 litres |
| 4 people | 36 litres | 84 litres |
| 5 people | 45 litres | 105 litres |
My advice: start with 3 days and then calmly build up to a week. That last bit is still perfectly doable and gives you a good deal more peace of mind.
Do you have a baby, pets or someone who takes a lot of medication with water? Then add a few extra litres on top. A cat or dog drinks too, and you can’t make up formula without water.
Drinking water or utility water: what’s the difference?
A lot of people miss this, and it saves you a heap of storage space.
Not all the water you use needs to be drinking-water quality. There are two kinds:
Drinking water. Water that goes into your body: drinking, brushing teeth, cooking food, baby formula. This really has to be clean.
Utility water (flushing water). Water for flushing the toilet, mopping the floor or rinsing something off. This doesn’t need to be drinking-water quality.
Why is that handy? Because for utility water you can build up a separate, more generous reserve that doesn’t have to be so pristine. Think of a filled jerrycan or two, or the water that’s already sitting in the house anyway.
| Use | Which water | Quality requirement |
|---|---|---|
| Drinking, cooking, brushing teeth | Drinking water | High, must be clean |
| Baby formula | Drinking water | High |
| Flushing the toilet | Utility water | Low |
| Mopping, rinsing, washing | Utility water | Low |
A classic prepper tip: before you flush the toilet, you can pour a bucket of water straight into the bowl. That flushes it through too, without needing your cistern or the mains. No clean bottled water required for that.
What do you store an emergency water supply in?
The container matters more than people think. Store water in the wrong vessel and after a few months you’ve got a musty, plastic-tasting mess.
You have roughly three options.
Jerrycans (food-safe). My favourite for the basics. Buy specific, food-safe water jerrycans of, say, 10 or 20 litres. They’re stackable, seal well and last for years. Look for the glass-and-fork logo (food-safe) on the bottom.
PET bottles (shop-bought spring water). Ready-bought bottled water is the easiest: just put it in the cupboard and you’re done. It usually keeps longer than water you’ve filled yourself. Check the best-before date on the bottle.
Self-filled tap water. Fine and the cheapest, as long as you do it right. Tap water here is top quality. More on that below.
What you don’t do: store water in old milk cartons, juice or squash bottles. Sugar and protein residues stay behind in those, and they’re a breeding ground for bacteria. Empty detergent or chemical containers are a no as well, however well you rinse them.
How do you store tap water safely for the long term?
Filling your own works excellently. Here’s how to do it in four steps:
-
Take a clean, food-safe jerrycan or bottle. Rinse it out beforehand with hot water, no soap.
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Fill it right up to the brim with cold tap water and screw the cap on tight. The less air inside, the smaller the chance of bacterial growth.
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Put a date on the jerrycan. A piece of tape with the fill date on it is enough. That way you’ll know exactly how old the water is later.
-
Store it cool and dark. This is crucial.
On that last point: temperature and light determine everything.
Store your water cool (around 10 to 20 degrees) and dark. A cool pantry, a cellar cupboard or a cool hallway indoors is ideal.
Do not put it in the shed or the garden house. It gets blistering hot there in summer and freezes in winter. Heat and light make algae grow and cause the plastic to leach into your water.
Shelf life of self-filled tap water: about 6 months. After that, replace it. It isn’t necessarily dangerous by then, but the taste and freshness go downhill.
Shop-bought bottled water often keeps for 1 to 2 years; just look at the date on the packaging.
Saving space? Combine large jerrycans for at home with a few small bottles you can quickly toss in a bag if you do have to leave. Stacking is perfectly fine, as long as the bottom jerrycans carry the weight. A full 20-litre jerrycan weighs 20 kilos, so put it down low.
How do you refresh your water supply?
Water isn’t meant to sit around forever. So rotate it.
The rule of thumb: check every six months and replace self-filled water.
Handy trick: tie it to the change of seasons or to the clocks going forward and back (spring and autumn). That way you won’t forget.
Here’s how to handle the rotation:
- Check the container. Bulging jerrycans, a damaged cap, discolouration or an odd smell? Throw it out and refill.
- Don’t just pour old water away. Use it to water the plants, wash the car or flush the toilet. Shame to waste it.
- Refill straight away with fresh tap water and put a new date on it.
With shop-bought bottled water you only need to watch the best-before date. Put the oldest bottles at the front, just like in the supermarket.
What other reserves do you have in the house?
Before you panic that your supply has run out: there’s often more water in the house than you think. Handy to know.
The hot water tank. A tank easily holds 80 to 200 litres of water. You can get at it in an emergency via the drain tap at the bottom. Let it cool first and switch off the power or gas. Note: with an old, scaled-up tank this water can contain sediment, so purify it to be safe (see below).
The water pipes in the house. There’s still water sitting in your pipes. Open the lowest tap in the house (downstairs, for instance) and let air in through a high tap.
The toilet cistern. The water in the cistern (not the bowl) is just clean tap water. Fine as utility water, and after purification more than that if needed.
A water butt. Rainwater is a fine reserve as utility water and, after proper purification, as drinking water too. Collect it in a clean water butt. If you want to set up a water butt or water store yourself, that’s a pleasant and useful little job. More on that further on.
What you don’t use: the limescale-heavy sediment at the bottom of an old hot water tank without purifying it, and pool water straight (that’s full of chlorine and other chemicals). Water from your central heating system is an absolute no too, as it often contains corrosion inhibitor.
How do you purify water when your supply runs out?
Suppose the emergency is bigger than expected and your supply is running low. Then you’ll want to be able to make water from another source safe. There are three reliable methods.
Important first: is the water cloudy? Then filter it first through a clean cloth or coffee filter. Purifying works a lot less well on dirty, cloudy water.
1. Boiling
The simplest and safest method if you have a heat source.
Bring the water to a vigorous boil and let it boil hard for at least 1 minute (a proper rolling boil). If you’re high up in the mountains, then 3 minutes, but that’s rarely an issue here.
Boiling kills bacteria, viruses and parasites. Let it cool afterwards. A musty taste? Pour it back and forth between two jugs a few times, and oxygen gets back into it.
2. Chlorine drops or bleach
Handy if you can’t boil. Use unscented chlorine drops (such as Hadex) or plain household bleach with no additives.
| Agent | Dose per litre of clear water | Contact time |
|---|---|---|
| Chlorine drops (Hadex) | 2 drops per litre | 30 minutes |
| Household bleach (unscented) | 2 to 4 drops per litre | 30 min (60 min for cold water) |
Stir well, put the cap on and let it stand for at least 30 minutes (60 minutes for cold water). A slight chlorine smell is normal and means it’s worked. Don’t smell anything? Repeat the dose.
Don’t use more drops than needed. Too much chlorine is unhealthy and tastes foul.
3. Water filter
A good emergency water filter (for example a portable one with ceramic or hollow fibres) removes bacteria and parasites, even without power.
Note: a simple filter doesn’t always remove viruses. To be safe, combine a filter with boiling or chlorine if you’re drawing from surface water or rainwater.
A filter is especially handy on the move or when you need to purify a lot of water quickly. For at home, boiling is usually enough.
Where do you store your emergency water supply?
One more practical word about the spot.
- Cool and dark: pantry, cellar cupboard, cool hallway or under-stairs cupboard.
- Reachable: not right at the back, because you have to get at it in the dark and without power.
- Away from chemicals: keep your distance from cleaning products, paint, fuel and pesticides. Plastic breathes a little and picks up smells.
- Not in freezing cold: freezing water bursts your jerrycans.
Split your supply across two spots if you like. Then you’ve still got something in reserve if one spot becomes unreachable.
Frequently asked questions
Exactly how much water do I need per person?
Plan for 3 litres per person per day: 2 litres for drinking and 1 litre for cooking and hygiene. For 3 days that’s 9 litres per person, so 36 litres for a family of four. Build this up to a week at your own pace (21 litres per person).
How long does tap water keep in a jerrycan?
Self-filled tap water keeps for about 6 months if you store it cool, dark and well sealed. After that, replace it. Shop-bought bottled water usually keeps 1 to 2 years; look at the date on the bottle.
Can I just store tap water or do I have to buy bottled water?
Storing tap water is perfectly fine and much cheaper. Fill a clean, food-safe jerrycan right up to the brim, seal it well, put a date on it and store it cool and dark. Bottled water is only easier because you don’t have to replace it.
How do I clean water when my supply runs out?
Boiling is the safest method: bring it to a vigorous boil for at least 1 minute. If you can’t boil, use 2 drops of chlorine (Hadex) per litre of clear water and let it stand for 30 minutes. Filter cloudy water through a cloth first.
Can I use the water from my central heating or pool?
No. Heating water often contains corrosion-inhibiting chemicals and pool water is full of chlorine and other agents. Neither is suitable, not even after purification. Hot water tank water is fine, as long as you purify old, limescale-heavy sediment.
How often should I check my supply?
Every six months. Tie it to the change of seasons or the clocks changing, so you don’t forget. Replace self-filled water, check containers for damage and throw out water with an odd smell or colour.
In short
Building an emergency water supply really isn’t a big project.
- 3 litres per person per day, at least 3 days (72 hours).
- Store it in food-safe jerrycans or bottles, cool and dark.
- Self-filled water: replace every six months. Shop-bought water: watch the date.
- Know your reserves: hot water tank, pipes, cistern, water butt.
- You can purify: boiling (1 min), chlorine (2 drops/litre) or a filter.
Start small, with a few jerrycans for three days. That’s quickly sorted and it gives instant peace of mind. Building up to a week you can do later.
Not panicky, just prepared.
Want to set up a water butt or water store in the garden yourself as an extra reserve? That’s a fine little job to take on.
Want to know more about self-reliance and DIY? Have a look at fredsdiyplans.com.