Hydrostatic Level transducers are simple, rugged and inexpensive level sensors with built-in 4-20 mA transmitters with an IP68 rating they are at home in everything from clean water to activated sludge and Class 1, Div 2 environments. Moreover we can customize every single sensor (included in the price) for the depth range you require.
For clean water the AM-HLT-0 features a recessed membrane that is protected from sharp objects and is the most economical sensor. For wastewater the AM-HLT-5 has a flush, rugged membrane to prevent fouling. For wastewater with lots of suspended solids (such as sludge) the AM-HLT-50 has a large membrane and a protective aluminum plate.
These sensors output a 4-20 mA signal so they only connect to a PLC or an inexpensive panel meter to work. They come with an aneroid bellows that keeps the inside of the sensor dry. For less than $100 list price you can add lighting protection that comes with a lifetime guarantee against lightning damage. You will not find a more cost effective method for measuring liquid depth.