Water resistance is measured by subjecting a product to controlled water pressure and checking whether any moisture gets inside. The exact method depends on what’s being tested: electronics use standardized spray and submersion tests, watches use pressurized chambers, and fabrics use a column of water pushed against the material until it leaks through. Each industry has its own rating system, but they all boil down to the same physics: water pressure increases by about 1 atmosphere for every 10 meters of depth, and a product’s water resistance rating reflects how much pressure it can handle before failing.
IP Ratings for Electronics
If you’ve seen a rating like IP67 or IPX4 on a phone, speaker, or fitness tracker, that’s the Ingress Protection code. The first digit measures dust resistance, and the second digit (the one after the “X” or the second number) measures water resistance on a scale from 0 to 9. Each level has a specific lab test behind it.
At the lower end, IPX1 and IPX2 only protect against dripping water. The test simulates light rainfall (1 to 3 mm per minute) for about 10 minutes. IPX3 and IPX4 handle water sprays from various angles, tested with a nozzle delivering 10 liters per minute at pressures up to 150 kPa. The difference between the two is that IPX4 removes a protective shield used in the IPX3 test, meaning the spray hits the device more directly.
IPX5 and IPX6 test against water jets. IPX5 uses a 12.5 liter-per-minute jet at 30 kPa from 3 meters away, while IPX6 ramps that up to 100 liters per minute at 100 kPa. IPX6K goes further, blasting 75 liters per minute at 1,000 kPa, which is about 150 psi.
IPX7 is where submersion testing begins. The product sits underwater for 30 minutes at a depth of 1 meter. IPX8 goes deeper, typically up to 3 meters, with the exact depth and duration agreed upon between the tester and manufacturer. This is why you’ll see companies specify “IPX8: up to 2 meters for 30 minutes” on their own terms. At the top of the scale, IPX9K tests against high-pressure, high-temperature water jets (80°C water at 80 to 100 bar) sprayed from close range, a test designed for equipment that gets steam-cleaned in industrial settings.
One important detail: these ratings don’t automatically stack. A device rated IPX7 (submersion) hasn’t necessarily passed IPX6 (high-pressure jets). When both protections are verified, you’ll see a dual rating like IPX6/IPX7.
How Watch Water Resistance Is Tested
Watch water resistance uses a different system measured in atmospheres (ATM), bars, or meters. One ATM equals roughly 10 meters of water pressure. A watch rated at 5 ATM can withstand static pressure equivalent to 50 meters of depth, and 10 ATM corresponds to 100 meters. These numbers describe pressure tolerance, not actual diving depth, because real-world wrist movements create additional force that static ratings don’t account for.
Two ISO standards govern the testing. ISO 22810 covers general water-resistant watches and lets the manufacturer define the overpressure level. A watch can be tested at as little as 2 bar for 10 minutes under this standard. There’s no minimum depth requirement. ISO 6425, which governs professional dive watches, is far stricter. It requires at least a 100-meter depth rating and includes a thermal shock test: the watch is submerged in 40°C water for 10 minutes, then moved to 5°C water for 10 minutes, then back to 40°C for another 10 minutes, after which it’s checked again for leaks.
Professional watchmakers test water resistance using two main approaches. A “wet” test places the watch in a pressurized water chamber and checks for bubbles or moisture inside the case. A “dry” test pressurizes the chamber with air instead. In the dry method, a sensitive gauge rests on the watch crystal. If the case leaks, the crystal flexes slightly under pressure, and the gauge detects that movement. Dry tests are preferred for routine checks because they don’t risk getting water inside an otherwise functional watch.
Fabric Waterproof Ratings
For jackets, tents, and outdoor gear, water resistance is measured using a hydrostatic head test. A tube is placed over the fabric, sealed at the edges, and water is slowly added. The column of water rises, increasing pressure on the fabric until droplets push through the other side. The height of the water column at the point of failure, measured in millimeters, becomes the fabric’s waterproof rating.
A rating up to 5,000 mm handles light rain. Between 5,000 mm and 10,000 mm covers average to heavy rain. Anything above 10,000 mm is suited for very heavy, sustained downpours. In the UK, a fabric must achieve at least 1,500 mm to be labeled waterproof. High-performance outdoor gear often reaches 20,000 mm to 30,000 mm. These tests follow standards set by organizations like ASTM and ISO to ensure consistency across manufacturers.
Industrial Leak Testing Methods
Manufacturers who need to verify water resistance on a production line often skip water entirely. The most common industrial method is pressure decay testing. The product or component is filled with pressurized air, then sealed off from the air supply. After a stabilization period, sensors measure whether the internal pressure drops over a set time window. Any drop means air is escaping through a gap or imperfection, which means water could get in the same way. The rate of pressure loss tells engineers how significant the leak is. If pressure holds steady, the seal is intact.
This method is fast, repeatable, and doesn’t leave moisture inside the product. It’s widely used for testing phone housings, sealed connectors, medical devices, and automotive components before they ever receive an IP or ATM rating.
Testing Water Resistance at Home
For watches specifically, DIY pressure testers are surprisingly accessible. The basic setup involves a clear water filter housing (about $33), a few plumbing fittings, and a bicycle pump or air compressor, for a total cost around $40. You fill the chamber with water, hang the watch inside on a bent coat hanger, seal the housing, and pressurize it with the pump. If the watch leaks, bubbles will form visibly around the case. If no bubbles appear, the seals are holding.
Before pressurizing, it’s worth checking your own setup for leaks first. Mix a drop of dish soap with a small amount of water and pour it over the fittings. Bubbles at a fitting mean you need more PTFE (plumber’s) tape on the threads. Once the housing holds pressure without bubbling at the joints, you can trust the results for the watch inside.
This kind of test can verify pressure resistance up to about 10 ATM (100 meters equivalent), depending on the housing’s rated capacity. It won’t replicate the thermal shock or long-duration tests of ISO 6425, but it’s effective for checking whether a watch’s gaskets are still sealing properly after a battery change or years of wear.
Why Ratings Degrade Over Time
Water resistance is not permanent. The rubber gaskets and adhesive seals that keep water out slowly break down from UV exposure, temperature swings, and repeated physical stress like button presses or crown adjustments. Saltwater and chlorine accelerate this process. The chemicals in pool water and ocean salt can corrode seals and damage surface finishes if not rinsed off after exposure. A watch rated to 100 meters when new may fail at far less after a few years without maintenance.
The same applies to electronics. A phone’s IP68 rating reflects factory-fresh seals. Drops, screen repairs, and normal aging reduce that protection in ways no rating captures. Fabric waterproofing degrades too, as the durable water repellent (DWR) coating on the surface wears off from washing and abrasion, even though the underlying fabric may still pass a hydrostatic head test. Reapplying a spray-on DWR treatment restores the outer layer’s ability to bead water rather than letting it soak into the fabric and overwhelm the membrane underneath.