When is a metre not a metre?

I recently purchased a new watch. My previous one has seen 12+ years of active service and was starting to have a couple of problems. The previous watch is water resistant for 50 metres, but the new one is water resistant to 100 metres. This wasn't a feature that I was looking for on either watch, but it's handy to know that you don't have to worry about it getting wet during the course of a normal day.

It is a feature that I've wondered about. Who needs a watch that will work in 50m of water? Nevermind 100m - or 200m or even 1000m. Just to put it in context, most swimming pools might have a deep end of 2m or 3m. A diving pool with a 10m board might be up to 5m deep. The Royal Navy in the UK have a tower for practising escaping from submarines. This allows them to do 30m ascents. The world record for free diving is 214m!

I was on the Seiko web site, and while perusing their FAQ I found this useful information about water resistance in watches. Basically, a watch which is resistant at 50m is only resistant at 50m if it's not moving. The watch should be static and the water should be static. If either of them is moving then the pressure is different and there could be leakage.

Q: What exactly does the water resistance description on my watch mean?

A: The Water resistance relates to pressure as measured in the equivalent of a static tank of water at a given depth under water. But please note, the faster an object is moved in or against water, the greater the pressure on the watch. For that reason, a watch that is water resistant
to 30 metres may leak if exposed to water coming forcefully from a tap, or worn whilst viourously swimming or diving, as the increased pressure may exceed the designed resistance.

So according to them, your cool watch which is good to 30m (the same distance as you might escape from a submarine, as you do), mightn't last washing the dishes if you have the tap on too high.