water depth measurement

How much range? What type of liquid? How accurate? The more details the better...

A simple float works well and is time proven just like they use for gas tanks in cars... You can attach the float to a lever that rides along a linear digital scale and you can get damn accurate readings to the 100oth of an inch easily... You can also use an ultrasonic distance module and bounce it off the top of the water from a fixed height... Or there are fancy proprietary sensors used in the food and other industries to measure liquid levels, lots of options...

 

you could use pressure if its sealed, a float etc... but no matter what we need to know dimensions of tank or else all you will get is empty,low, full type things maybe if you are lucky a percentage

 

Ultrasonic distance measurement often used in industrial processes

 

there are a few possibilities.if its just depth then the easiest is ultrasonic.

 

Others' experience is that the ultrasonic transducer needs to be on the bottom of the tank or pool, so that the reflection is from the surface. Anyway this worked well at Speights brewery in Dunedin with beer as the liquid of interest.
(This interest I mentioned is quite apparent in some "Daves",)