Hi,
according to the datasheet you mentioned in your initial post that sensor isn't a differential pressure sensor, since it has one pressure port only. Further that pressure port is "open" meaning no way to connect a hose to it. You might use that one to construct an altimeter.
Pressure sensors are designed to measure air pressure. Under no circumstances dunk a pressure sensor into water. It will be destroyed the moment it submerges.
It should be mounted well above the highest expected water level.
You'd be better off using an MPX5500DP. Maxim pressure 500KPa. "DP" stands for dual port, meaning it is fitted with two plastic pressure ports to connect hoses to them.
To measure the actual water pressure it requires to sense the water pressure on the positive pressure port and atmoshperic pressure on the negative pressure port, resulting in true water height regardless of loacal air pressure variations, which might fall to 850HPa in a low weather system and rise to 1,100HPa in a high.
Additionally, using a single port pressure sensor the measured pressure will always be difference between water pressure and standard atmospheric pressure which is 1,013.2HPa.
For better understanding I attached a small drawing showing water level detection. It works the same way detecting water pump pressure.
Pic2 shows a dual port differential pressure sensor.
Boncuk