In air the sensor works from 10-80 cm and you want to get 2 feet ~50 cm through water??
My guess is that if you have the sensor above the water it will tell you the distance to the water, and if you put it underwater as is it short out.
I have stated a couple of times that water greatly attenuates the IR signal but you keep asking about it so I would recommend you buy one of these sensors and try to see performance you get. The sensors are pretty cheap in the US, can't say for other sources.
I spent a good chunk of my career working many aspects of IR detection and propagation and it would a lot easier for me to buy the sensor and test its performance than try to predict the performance with high accuracy. But I will say my gut feeling is this sensor will not work for at 2 feet, but you should buy and test its performance and let us know what the performance was in a future email.