Water restrictions on airplanes have long been a source of frustration for passengers. While other drinks like soda and juice are permitted, water bottles must often be surrendered at security or emptied before boarding. This seems odd given that water is generally regarded as harmless. So why exactly are water restrictions in place on airplanes?
The Security Risk of Liquids
In August 2006, British authorities foiled a terrorist plot to detonate liquid explosives smuggled onboard planes headed from the UK to the US and Canada. This led to a sudden ban on all liquids, aerosols and gels in carry-on luggage. The ban caused chaos at airports as passengers had to discard all drinks, cosmetics, medicines and other essential items before passing through security.
The liquid ban was eventually relaxed later that month to allow small quantities of liquids, gels and aerosols. But each container could only hold 100ml or less and all had to fit inside a single, clear, resealable plastic bag no larger than 20cm x 20cm. This container size limitation remains in place today as authorities believe larger volumes of liquid could be used to create dangerous homemade explosives.
Why 100ml?
The 100ml limit was not chosen arbitrarily. According to the UK government, this volume was deemed sufficiently small that it would limit the damage caused if used to create an improvised explosive device while in flight.
With only 100ml, there is a limit to the quantity and concentration of chemicals that can be carried through security. This restricts the size and scale of any potential liquid bomb, thus reducing the risk of a successful terrorist attack.
Why Are Liquids Seen as More of a Risk Than Solids?
Liquids, aerosols and gels are viewed as a greater security risk than solid items because they can be combined and manipulated more easily to create homemade explosives. Solids have less room to hide dangerous chemicals and are harder to convert into bombs.
Liquid explosives can resemble harmless everyday products like drinks and toiletries. But when mixed together using a special process, relatively small quantities can create substantial detonations. Thankfully, the complexity involved means most passengers lack the chemistry knowledge to create liquid bombs.
Why Can’t You Take Large Volumes of Water?
Water is subject to the same 100ml limit as other liquids. But why can’t larger volumes be permitted given that water alone poses no obvious risk? Would allowing extra water really increase the terrorist threat?
There are a few reasons large volumes of water are also restricted:
- Water could be used to dilute other chemical ingredients for an improvised explosive device. More water means the ability to transport greater quantities of dangerous liquids.
- Water bottles could be used to conceal hazardous liquids with water simply acting as a cover. Restricting water reduces the opportunity for such deception.
- Having an exception for water would make security screening more complex as staff would have to differentiate harmless water from potentially dangerous liquids.
- Allowing some larger liquids but not others could cause confusion, arguments or accidental security breaches.
- A universal liquid size limit creates a simple, unambiguous rule that is easier for passengers to understand and comply with.
Therefore, while water itself poses minimal risk, permitting larger volumes could enable more threatening liquids to be smuggled or provide cover for prohibited items. A consistent rules for liquids enhances security and reduces screening complexity.
Why Can’t You Take Empty Water Bottles Through Security?
Empty water bottles are also prohibited in carry-on luggage by most airlines. This may seem especially odd given that empty bottles are harmless. But there are a few reasons behind this restriction:
- Empty bottles could be filled from water fountains after passing through security, allowing large volumes of liquid to be taken onboard.
- Empty bottles could be filled with other prohibited liquids after screening.
- Having an exception for empty bottles increases the complexity and subjectivity of security screening.
- Terrorists could try to pass filled bottles off as empty.
- Limiting empty bottles reduces potential confusion over regulations.
So empty water bottles are usually confiscated for some of the same reasons large volumes of water are not permitted. Preventing empty containers being filled after screening is another way authorities limit the quantity of liquids permitted in the secure zone of airports.
What Liquids Are Allowed in Carry-On Bags?
The 100ml liquid limit does not mean liquids are completely prohibited. Passengers are permitted reasonable quantities for use during their flight. Examples of liquids, aerosols and gels that can be taken through security in containers 100ml or less include:
- Water, juices and other drinks
- Liquid medicines and pharmaceuticals
- Hand sanitizers
- Contact lens solution
- Perfumes
- Essential toiletries like toothpaste, shampoo and shaving cream
- Hairsprays, mascaras and other cosmetics
- Food items like soup, syrups and oils
Each container must comply with the 100ml limit. However, passengers can carry as many 100ml or smaller containers as can reasonably fit inside a 20cm x 20cm plastic bag. Ziplock and clear resealable bags are permitted, while opaque bags and those with bigger capacities are not allowed.
| Allowed | Not Allowed |
|---|---|
| – 100ml water bottle | – 200ml water bottle |
| – Contact lens solution | – Can of shaving cream |
| – Travel size toothpaste | – Full size shampoo |
| – 60ml bottle of perfume | – Opaque plastic bag |
| – Clear 1L resealable bag | – Grocery bag |
The quantity restrictions mean most passengers cannot carry their normal full-size toiletries. But essential medical supplies like insulin or baby food and milk are often permitted exceptions in larger volumes than 100ml.
Duty Free Liquids
Liquids purchased from airport duty free stores are also exempt from the restrictions. However, duty free liquids are sealed in special tamper-evident bags that are only allowed to be opened once you have reached your final destination. They must remain sealed while in transit.
Where Does the Liquid Ban Apply?
The 100ml liquid rule applies:
- At airport security checkpoints when passing into the secure zone before boarding flights.
- When boarding flights directly from non-airport locations like private jet terminals.
- When passing through security on domestic flights in some countries like Australia, even for carry-on luggage that has already been screened.
The liquid restrictions generally do not apply:
- Once aboard the aircraft.
- At customs/immigration when entering a country.
- On private flights where passengers and baggage are not security screened.
However, cabin crew can still confiscate large volumes of liquids or unsealed duty free liquids consumed during the flight.
Are All Countries and Airlines the Same?
Most major countries have adopted the 100ml liquid limit set by the UK and EU in 2006. But some exceptions include:
- The US limits liquids to 3oz (100ml) containers rather than 100ml.
- Some countries like Morocco have restrictions on lighter fuel only, with no limits on other liquids.
- In Egypt, only transit passengers are subject to liquid restrictions.
- Russian internal flights have no liquid limits but international flights do.
- Domestic flights within New Zealand and Australia often allow larger liquid volumes.
Some low-cost carriers also have more flexible rules allowing larger liquids in carry-on bags. But the 100ml limit is now standard across most of the world and airlines for international flights.
Are There Any Alternatives to Liquid Restrictions?
Technology like explosive trace detection (ETD) and X-ray scanners can detect threat liquids avoided restrictions. But these have significant limitations:
- ETD swab tests are time-consuming, disruptive and limited to small sample sizes.
- X-ray scanners cannot detect liquid explosives with much reliability.
- Advanced 3D X-ray machines are costly and slow down screening.
- New MRi-style scanners remain unproven for liquid threats.
This technology has improved but is still not at the stage it can replace liquid limits. Universal size restrictions therefore remain the most effective approach. However, future technologies like AI-enhanced scanners could allow a more tailored risk-based approach.
Has the Liquid Ban Prevented Any Attacks?
Authorities maintain the liquid explosives threat is ongoing. But it’s unclear if any specific attacks have been prevented solely due to liquid restrictions.
Intelligence reports suggest terrorists remain focused on targeting commercial aviation with improvised liquid-based devices. But no major liquid bomb plots are known to have breached security since 2006. This suggests enhanced screening and passenger awareness has likely deterred and disrupted attack plans.
Nonetheless, the ban remains justified. Liquid bombs require chemistry knowledge and experimentation so are beyond most passengers. But Al-Qaeda and other groups have shown interest and capability in developing liquid explosives making complacency dangerous.
Conclusion
Limiting liquids, aerosols and gels remains an essential aviation security measure. The inconvenience to passengers is regrettable. But a universal 100ml rule for carry-on luggage prevents dangerous chemistry experiments aboard aircraft. It allows rapid screening that balances both security and efficiency.
The liquid threat is still active even if no known plots have succeeded recently. As technology improves, restrictions may be refined. But for now, a clear size limit based on minimizing potential blast impacts remains the most effective approach. This rule continues to disrupt terrorist ambitions and keep passengers safe in the air.