

The water thing is just a quirk of capacitive touchscreens. The same happens on the most expensive watches too, which is why there is usually a water mode that you can put the watch into. It sorta locks the touchscreen until you disable it using one of the physical buttons.
Limiting the bandwidth use of individual devices is pretty easy, and basically standard procedure for public networks. Even cheap consumer routers that come with ISP subscriptions can do that.