RecolherSecção 03
Garrafão dobrável de 10 litros
Why: para recolher e transportar água; ocupa pouco espaço vazio.
Essential guide · Base level · 7 min
Essential guideBase level · open to all7 min read
Water beyond the tap: where to find it, how to collect it and what never to drink
When your supply runs out or you're away from home: the water hidden in your home, springs, streams and rain, what «uncontrolled water» means, and the water no home treatment can save — following the CDC.
Reviewed 1 Oct 2026
02·CWater beyond the tap
In 30 seconds
The essentials, in four points.
Home
Before looking for water outside, use what you already have: the hot-water tank, ice from the freezer and the toilet cistern, if it has no cleaning products.
Treat
Rain, springs, streams, wells and public fountains: always treat before drinking. A 1-minute rolling boil kills germs. The Safe water guide explains every method.
Chemicals
Water with fuel, chemicals or green algal scum has no home treatment — not boiling, not filtering. Find another source.
0.5–1 L
is what a solar still yields in 24 hours, according to the US Army survival manual. Survival tricks give little water: don't count on them.
01Why prepare
Your home supply runs out. The water around you isn't all the same.
In a long water outage, after an earthquake or a flood, or on a walk that goes wrong, stored water may not be enough. There's almost always water nearby: in your own building, in the rain, in a stream, at a public fountain. The problem isn't finding it — it's knowing which can be made safe and which can't.
At home, no water from the tap
Start with the water hidden in your home. Then rainwater collected in clean containers, always treated.
In the countryside
Streams and springs, away from farmland, roads and settlements. Always treat.
At a public fountain
If it has a sign saying Água não controlada (uncontrolled water), nobody monitors it. Treat it like stream water.
02First, at home
The water you already have and didn't know about.
Usable
Hot-water tank
The tank that feeds your taps holds dozens of litres. Switch it off first and let the water cool. Not the central heating tank.
Usable
Ice
Melted ice cubes made with mains water.
Usable
Toilet cistern
Only water from the cistern, never the bowl, and only if it's clean and has no tablets or cleaning products.
Usable
Tinned food
The liquid from tins of fruit and vegetables.
Don't drink
Pools and hot tubs
For hygiene and cleaning, not for drinking.
Don't drink
Floodwater
It can contain sewage, fuel and chemicals. It can't be made safe at home.
03Away from home
Choose. Collect. Treat.
Step 1
Choose
Clear, running water, away from farmland, roads, factories, settlements and animals. Never water smelling of fuel, with an oily film or green scum.
Step 2
Collect
With a clean container, upstream of where you've stepped. If it's cloudy, let it settle and strain it through a clean cloth.
Step 3
Treat
A rolling boil for 1 minute. Or a filter plus disinfection, as the Safe water guide explains.
Collecting rainwater
At home or outdoors1
Use a tarp, groundsheet or roof and clean containers with lids. A lower corner of the tarp channels the water into the container.
2
Rain falls clean, but doesn't arrive clean: roofs and tarps carry dust, leaves and bird droppings. Always treat it before drinking.
3
Cover the containers as soon as they're full, to keep out insects and dirt.
04What never to drink
Some water no home treatment can save.
1
Water with fuel or chemicals. Boiling, filtering or disinfecting doesn't remove fuels, chemicals or toxins. If you suspect them, there's no way to make it safe.
2
Water with green scum or film (algae). Some algae produce toxins that attack the liver. Boiling doesn't remove them.
3
Runoff from farmland, roads or industrial areas, for the same reasons: filters and boiling deal with germs, not chemicals.
4
Seawater. Your kidneys can't get rid of that much salt: to flush it out, you lose more water than you drank. Thirst and dehydration get worse.
5
Floodwater. A mix of sewage, fuel and chemicals.
05Six costly mistakes
Myths about water outdoors — and what to do instead.
Myth
“Spring water is always pure.”
It can carry germs from animals, septic tanks or fields. If it's not from the public network, treat it.
Myth
“If it's clear, it's clean.”
Bacteria, viruses and parasites are invisible. Clear water gets treated too.
Myth
“Boiling fixes everything.”
Boiling kills germs, but doesn't remove fuels, chemicals or algal toxins.
Myth
“A camping filter makes any water drinkable.”
Many filters stop parasites, but not all germs — and none remove chemicals. Add disinfection and choose your source well.
Myth
“A little seawater helps you hold out.”
It doesn't: the salt makes your body lose more water. Never drink seawater.
Myth
“A solar still will give me enough water.”
About 0.5 to 1 litre a day. It's a top-up, not a solution.
06Recommended equipment
Collect, carry and treat.
A collapsible container, a tarp and a way to treat water take up little space in a grab bag or day pack. To boil, add a camping stove — the Safe water guide has the full list.
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ChuvaSecção 03
Lona impermeável 3 × 3 m
Why: recolhe a chuva e serve de abrigo. Um canto mais baixo encaminha a água.
TratarSecção 03
Filtro de água portátil
Why: retém parasitas e sedimentos. Junta-lhe desinfeção: não retém tudo nem tira química.
TratarSecção 03
Pastilhas de dióxido de cloro
Why: desinfetam a água depois de filtrada, quando não dá para ferver.
TratarSecção 03
Fogareiro de campismo
Why: para ferver a água durante 1 minuto quando não há eletricidade.
Quick card
Print it. Keep it with your water supply.
Keep it by your home water supply, with a copy in the grab bag.
Water beyond the tap · K72 sheet
1At home: hot-water tank (off and cool), ice, toilet cistern with no chemicals
2Outside: clear, running water, away from fields, roads and settlements
3Always treat: rolling boil for 1 minute
4Cloudy: let it settle and strain through a clean cloth
5Never: fuel, chemicals, algae, seawater, floodwater
6Fountain signed Água não controlada = treat
02·C · k72plus.comEMERGENCY: 112
- CDC — How to find clean water in an emergency — hot-water tank, ice, cistern, tinned food; pools; outdoor sources to treat; chemicals can't be treated
- CDC — Water treatment options when hiking, camping or traveling — 1-minute boil, filters and disinfection, chemicals and toxins
- Águas de Santarém — Uncontrolled water (in Portuguese) — Decree-Law 152/2017, fountain signs
- Minnesota Department of Health — Water treatment in the backcountry — farm runoff, algal toxins, filter limits
- NOAA — Why can't people drink seawater?
- US Army — FM 21-76 Survival Manual, chapter 6: water procurement — solar still: 0.5 to 1 litre in 24 hours
Reviewed 1 Oct 2026 · Next review: Mar 2027 · Spotted a mistake? Tell us.
This guide does not replace advice from health authorities and your water supplier. In an emergency, call 112.