It sounds like confusion caused by this note that DJI put up a few months ago, causing folks to mistakenly believe that DJI Fly won't work on tablets any more.
Except that makes no sense at all.
People have been flying over water since DJI started selling drones and no-one has ever had any problem with radio waves getting scrambled.
Although DJI have that note on their website, it's completely untrue.
The app works perfectly on any compatible phone or tablet.
You have to download the app from DJI's website rather than the Android market.
Most of their current drones come...
The only issue is that the downward sensors may have trouble maintaining horizontal position if you fly low enough to the water.
But maintaining horizontal position is not real concern unless you are close to obstacles.