Hi yes there are several ways to do this as well as many other important pramiters that are esential to monitor the sub.
I use now for several years the Eagle Tree Seagull wireless telemitry sytem ,it works underwater and senses a huge variety of items from voltage usage at the servos to amps hours left on board to even the depth to mm resolotion and yes even if water of the smallest amount enters it will set off an alarm to warn you!
I love this system its so easy to use and veryflexable and easy to set up on any pc ,the cost under 300 bucks and only that amount at first as the brain box can be transfered to any model and not just subs but any kind of rc or even full sized machines can be monitored,a large sellection of sensors is available and at very resonable prices go tp Eagletree.com for more info.
It is the best system out there and well worth the money.

Dave