The Rule of Threes
Survival experts use this framework:
| Without | Survival Time |
|---|---|
| Air | 3 minutes |
| Shelter (harsh conditions) | 3 hours |
| Water | 3 days |
| Food | 3 weeks |
Water is second only to shelter in immediate survival priorities.
Daily Water Needs
| Situation | Per Person |
|---|---|
| Minimum survival | 1 litre |
| Comfortable survival | 2-3 litres |
| Including cooking/hygiene | 4+ litres |
UK Emergency Scenarios
"Survival" isn't just wilderness adventures. In the UK:
| Scenario | Likelihood | Duration |
|---|---|---|
| Major pipe burst | Common | Hours-days |
| Power cut (pumps fail) | Occasional | Hours-days |
| Flooding/contamination | Occasional | Days-weeks |
| Treatment plant failure | Rare | Days-weeks |
| Severe weather | Seasonal | Days |
December 2024: 130,000 Kent homes without safe water for 14 days. It can happen anywhere.
Emergency Water Sources (Ranked)
Safer Sources (Still Treat If Possible)
- Stored bottled water — safest
- Rainwater — relatively clean
- Hot water tank — safe if recently heated
- Toilet cistern (tank, not bowl) — clean if recently filled
- Freezer ice — melted, just frozen tap water
Risky Sources (Must Treat)
- Streams and rivers
- Lakes and ponds
- Puddles (last resort)
- Snow (requires lots for little water)
Avoid Completely
- • Swimming pools (chemicals)
- • Hot tubs (chemicals, bacteria)
- • Floodwater (sewage)
- • Near industrial sites
- • Stagnant water with visible contamination
Method 1: Boiling (Most Reliable)
The oldest and most effective method.
How To:
- Filter through cloth first (remove sediment)
- Bring to rolling boil
- Maintain boil for 1 minute (3 min at altitude)
- Allow to cool
What It Kills:
- Bacteria (E. coli, Salmonella)
- Viruses (Hepatitis, Norovirus)
- Parasites (Giardia, Crypto)
What It Doesn't Remove:
- Chemicals
- Heavy metals
- Sediment (filter first)
- Taste/odour
Requires: Heat source, fuel, heat-safe container
Verdict: First choice when fuel available.
Method 2: Chemical Treatment
Lightweight and effective for biological threats.
Household Bleach Method
Use: Unscented bleach, 5-6% sodium hypochlorite
| Water Type | Amount Per Litre |
|---|---|
| Clear water | 2 drops |
| Cloudy water | 4 drops |
- Filter through cloth first
- Add bleach
- Stir and wait 30 minutes
- Should have slight chlorine smell
Purification Tablets (Better Option)
Types:
- • Chlorine dioxide (Aquamira, Micropur) — kills everything including Crypto
- • Iodine — effective but avoid if pregnant/thyroid issues
Keep in your emergency kit: One bottle per person.
Method 3: Portable Filters
Gravity Filters
Water drips through filter element by gravity.
Pros
- • No pumping needed
- • Large capacity
- • Long filter life
Cons
- • Slow
- • Bulky
- • Most don't kill viruses
Examples: British Berkefeld, Doulton, Lifestraw Community
Best for: Home emergency prep, off-grid living
Pump/Squeeze Filters
Pros
- • Faster than gravity
- • Compact, portable
- • Very long filter life
Cons
- • Requires effort
- • Most don't kill viruses
Examples: Sawyer (400,000 litres!), Katadyn, MSR
Best for: Camping, hiking, personal emergency kit
Straw Filters
Pros
- • Ultra-compact
- • No prep needed
- • Cheap
Cons
- • Can't fill containers
- • Personal use only
Examples: Lifestraw, Sawyer Mini
Method 4: UV Treatment
UV light kills pathogens by destroying their DNA.
UV Pens (e.g., SteriPen)
How: Swirl pen in water for 90 seconds.
| What It Kills | Status |
|---|---|
| Bacteria | |
| Viruses | |
| Parasites |
Requirements: Must filter cloudy water first (UV blocked by particles). Needs batteries or charging.
Verdict: Excellent backup. Fast, no taste change. But needs power.
Method 5: DIY Filtration
When commercial filters aren't available.
The Layered Filter
Build in a container with drainage holes.
Bottom to top:
- Large gravel (support)
- Small gravel (large particles)
- Coarse sand (medium particles)
- Fine sand (small particles)
- Charcoal, crushed (chemicals, taste)
- Fine sand (final filter)
- Cloth (pre-filter)
⚠️ Important: This removes particles only. You MUST still boil or chemically treat the filtered water.
SODIS Method (Solar Disinfection)
Using sunlight and a plastic bottle:
- Filter through cloth
- Fill clear PET bottle (2L max)
- Shake to oxygenate
- Place in direct sun for 6+ hours
- UV radiation kills pathogens
Proven effective — used by millions in developing countries.
Limitations: Slow, needs clear bottles and sunshine.
Your Emergency Water Kit
Basic Kit (Every Household) — Under £30
| Item | Purpose |
|---|---|
| Bottled water (9L per person) | 3 days supply |
| Purification tablets (100) | Backup treatment |
| Metal pot | Boiling |
| Clean containers | Storage |
| Household bleach | Chemical treatment |
Enhanced Kit — £150-300
Add:
- • Gravity filter (British Berkefeld)
- • Portable squeeze filter (Sawyer)
- • UV pen (SteriPen)
- • Collapsible water containers
- • Water testing strips
How Much to Store
| Duration | Per Person |
|---|---|
| 3 days (minimum) | 9 litres |
| 1 week | 21 litres |
| 2 weeks | 42 litres |
| 1 month | 90 litres |
Family of 4, two weeks = ~170 litres. Plan accordingly.
EMERGENCY WATER TREATMENT
Save or print this:
BIOLOGICAL THREATS:
- • Boil 1 minute ✓
- • Purification tablets ✓
- • UV treatment (90 sec) ✓
- • Filter + chemical treatment ✓
CHEMICAL THREATS:
- • DO NOT USE contaminated water
- • Seek alternative source
- • Most filters don't remove chemicals
REMEMBER:
- Filter sediment first (cloth min)
- Treat for biological threats
- Store in clean containers
- When in doubt, don't drink it
Frequently Asked Questions
How long can you survive without water?
Generally 3 days, though this varies with temperature, activity, and health. In hot conditions or when active, dehydration becomes dangerous within hours.
Is rainwater safe to drink in the UK?
Freshly collected rainwater is relatively clean but may contain pollutants from the atmosphere and collection surfaces (roofs, gutters). Filtering and treating before drinking is recommended.
Do Lifestraw-type filters remove viruses?
Most straw and pump filters remove bacteria and parasites but NOT viruses. In the UK, waterborne viruses are less common, but for complete protection, combine filtration with chemical or UV treatment.
How often should I replace emergency water supplies?
Every 6-12 months. Even clean water can grow bacteria over time. Date your containers and rotate stock — use oldest first, replace with fresh.
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Keith Wilks
Water Filtration Specialist | 24+ Years Experience
Keith has spent over two decades helping people understand water quality and find practical solutions for their homes. He believes in honest, evidence-based advice.
Read full bio →Last updated: January 2026. We review and update our content regularly to ensure accuracy.