Rain gauges measure the millimetres of rain fallen over a certain period of time.
Hydrometers detect the water level of rivers and lakes against a fixed reference (hydrometric zero).
Current meters measure the flow of water passing through a given river section over a certain period of time.
Level and pressure gauges measure respectively the water level in a reservoir and the water pressure in a pipe, converting these data into signals visible both on site or by a remote transmission and control system.
Weather stations include a set of measuring instruments which monitor the physical conditions of the atmosphere in a certain location for weather and climatic purposes. These are useful to collect data for interpretation and predictive models of processes related to water availability from sources.