Waterproofing explained

The latest, greatest phones can now survive a dip in the pool. But how manufacturers create and define "water resistance" may surprise you.

Plop.

That's the sound of your phone impacting a pot of tomato sauce. Or a swimming pool. Or -- God forbid -- a toilet bowl.

Normally, you're screwed. Unless you're very, very lucky (and have some silica gel packets handy), your phone's delicate circuits are toast.

But if you've got a water-resistant phone like the new iPhone 7, Galaxy S7, or Sony Xperia XZ, things could be way different. Just rinse off that tomato sauce -- with more water -- and you're back in business.

How water resistance works

iFixit teardown engineer Scott Havard asks us to picture an egg: a perfect, unbroken shell. There's no place for water to get in.

Now replace that egg with a plastic Easter egg, and you begin to see the difficulty.

That's a lot of holes to protect.

"If you have an Easter egg that can break into two parts, all of a sudden the game changes," says Havard. Water goes to the place of least resistance -- the gap between the shells -- and sometimes, it can get through. "With enough pressure, you can push water molecules into the device," says Havard.

But your phone doesn't just have one gap. It has many. Every single port, button, speaker grille, and microphone hole could be the weakest link that lets water into your handset. That's not to mention the giant gap between the rim of your phone and its glass screen.

Havard says modern, brittle glass screens pose a particularly hard problem for water-resistance since manufacturers can't permanently attach them to the frame.

So manufacturers use a surprisingly simple technique: glue. Lots of it.

They're called gaskets, seals, tapes or adhesives, but it all means the same thing: manufacturers use sticky, rubbery glue-like substances to create an airtight seal.

Just look at any teardown of a water-resistant handset: you'll see a thick, sticky substance that cements the screen to the chassis. Manufacturers also use dabs of glue at the back of ports (typically where USB, Lightning, and 3.5mm headphone jacks connect to the motherboard) and sometimes on top of exposed circuits near the edges of the frame.

Glue doesn't work for everything, though: you wouldn't want visible goop oozing out where buttons, ports, and removable components stick out of the phone.

That's where rubber gaskets come in: little O-rings that press up against the inside of the device, expanding as they're firmly fastened (squished) against the inside surface.

You'll find the rubber rings around a phone's headphone jack and charging port, and there's typically a tiny rubber gasket around the SIM card tray. Apple even uses the rings around some cable connectors as an extra insurance policy.

For buttons, manufacturers may use a different technique: a little boot of silicone rubber that completely separates the physical part you push from the electrical contacts inside. It's a little bit like covering your shoes with a plastic bag before stepping out onto the wet sidewalk. That goes for the little button you push with a paper clip to pop out your SIM card tray, too.

Watertight, not airtight

But a few parts of the phone mustn't be completely sealed.

Speakers and microphones need air to enter and leave your phone because creating vibrations in the air is how they produce sound. Plus, if a phone is completely airtight, the pressure inside the phone might not be equal to the outside, creating an opportunity for that pressure to breach the phone's seals and let the water 

How do they keep water out? Science! Many manufacturers of water-resistant phones place an incredibly fine mesh in front of their speakers and microphones, prompting the water to follow its natural tendency -- through cohesion and surface tension -- to "stick to itself" rather than passing through.

And in some cases, like the bottom-left speaker grille on the iPhone 7 or the Galaxy S7's microphones, manufacturers use a fancier pressure vent as well.

Instead of just a mesh, they add a water-resistant, breathable fabric membrane (ePTFE) to let air through and equalize the pressure. (Gore, the maker of ePTFE material Gore-Tex -- yes, the same fabric you'll find in your ski jacket -- tells CNET it's sold over a billion portable electronics vents to date.)

Some manufacturers, like Samsung, even protect their charging ports from shorting out by automatically switching them off, and use corrosion-resistant metals (like nickel) to keep rust from wearing phones down.

That's why modern water-resistant devices don't need finicky port covers to keep the water out.

There's no such thing as waterproof

The problem is, none of these techniques are enough to keep water out indefinitely. There's no such thing as a waterproof phone.

"With enough pressure, water will travel through; it's just a matter of how much is needed," says iFixit's Havard.

That's why Apple, Samsung, and Sony are so insistent on the phrase "water-resistant" instead of "waterproof."

But there's also the little matter of water with added chemicals. For instance: salt.

Sony used to proudly advertise that you could take pictures underwater with its Xperia phones. But in 2015, Sony got in trouble with Australian regulators and citizens who claimed the phones stopped working (and even rusted) after a swim in the pool. What Sony may not have counted on: Australia's home swimming pools typically use salt water, which can corrode and breach the seals of a water-resistant phone.

Practically overnight, Sony changed its tune -- it started explicitly telling people not to use their phones underwater, and to keep them far away from salt.

And while Sony's stance has slightly softened since ("If you want to use your device to get underwater close-ups of a spectacular dive or your child's first swimming lesson, go ahead," read the company's current guidelines), the company says that advice only applies to chlorinated freshwater (not salt) swimming pool, with an IPX8-rated phone (more on that in a sec), and that you need to rinse off the chlorine with fresh water afterward.

Meanwhile, Apple has a whole list of things you shouldn't do with a water-resistant phone.

When companies say their phones are water-resistant, here's what they really mean: the phone was able to withstand a certain amount of water for a certain period.

How much? It depends on the IP ratings.

Suffice it to say water-resistant phones are tested to see if they can:

• survive droplets of freshwater
• survive jets of freshwater
• survive being gently submerged in a few feet of water for a prolonged period (e.g., 30 minutes)

And that's about it.

(If you're sitting on the bottom of a swimming pool for half an hour, you've got bigger issues.)

But that (and protection against dust) is all an IP rating guarantees, and it only proves a manufacturer managed to pass those tests in their lab. It says nothing about being able to actually use a phone underwater, or drop a phone into the water instead of gently submerging its frame, or with other types of liquid.

The IP ratings also don't guarantee that your phone will still be able to survive water after a bit of wear and tear or even simply sitting out on a shelf.

And they don't guarantee that your phone will immediately work after a dip. (For instance, Apple recommends you let a phone dry for at least five hours before attempting to charge it.)

Thank you for reading!

Credits: Cnet