# How is water resistance of a device measured?

This question has relation to physics as well, but since it is electronic related, it is here.

I was watching a video that is testing the water resistance of Apple Watch. They say, at 3 feet the watch can stand for 30 minutes.

So, if I was to be developing an electronic device, how am I suppose to determine how water resistant my device is? Probably I wouldn't be putting multiple of my devices in water again and again for testing to see how long it can stand, right?

As far as I understand, 3 feet determines the water pressure.

• look up ip rating (ingress protection) Apr 26 '15 at 15:58
• Putting multiple samples of your device through water spraying and submersion tests is exactly how you prove a water resistance rating or IP liquid ingress protection rating. See, for example: youtube.com/watch?v=3u9ld3AFlRA Apr 26 '15 at 16:11
• The question title could be reworded to avoid misunderstanding that it is about measuring the resistance of water which happens to be about 182 kΩ·m at 25 °C if it is ultra-pure. Apr 26 '15 at 18:07

You are right, the depth is essentially telling us the pressure the watch can withstand. Overall there are 2 tests performed, specifically on watches.

1. Dry test

In this test the watch is place in an airtight chamber and the pressure is increased. If there is any change in the dimensions of the watch then it is not resistant at that depth.

Once we determine a watch is not water resistant the next test is usually performed to determine at which point the watch is failing.

1. Wet test

The watch is placed in a chamber half filled with water and air. The pressure of the air is gradually increased and the watch is then immersed into the water. The pressure is now released. If bubbles come out the watch is not water resistant. The location of the bubbles is the fault location. (essentially what you do when you get a tyre puncture fixed).

You can easily perform these tests on your electronic equipment (in a protective casing), first doing the dry test. If you do not see any noticeable fault you can try the wet test.

(If you are really ambitious i guess you could always pay a diver to take it to that depth!)

Reference:

http://www.prestigetime.com/page.php?water-resistance

• You should be able to do most of the testing without necessarily putting all the expensive stuff in the case. Apr 26 '15 at 18:07