Water Level Indicator : 5 Steps (with Pictures) - Instructables
Level Sensor Switch Capacitive Probe Arduino For Water Tank Alarm And Solids Capacitance Type Liquid Controller - Buy Point Level Switch For Bulk Solids Capacitance Fuel Level Sensor/level Switch For Diesel Fuel
Optical Liquid Level Sensor
Sensor for underground water tank level - Arduino Stack Exchange
Arduino water level/quantity/volume indicator/monitor/measurement in water tank