Hydrology is the science of water in the Hydrological or water cycle and is concerned with its states, storages and  fluxes  in location, time and phase. Hygrometry is the sister science of hydrology which is concerned with the measurement of these states, storages and fluxes in the water cycle. It is a science because it is concerned with the scientific principles of repeatability and that measurements may be checked and validated.

Three key features of information are reliability, availability and presentation. Information is data which has been manipulated and processed to give them meaning and purpose. By definition, information serves a function and is created not simply because it is there to be measured or because of our curiosity alone. Unlike the mountaineer, we are not climbing Everest simply because it is there to be climbed- but because there is someone on the top who needs help. Function is important, not only in establishing the contents and structure of the information but also as a motivation for all involved in the development and maintenance of the HIS.

System:        

The HIS is not simply a data collection or archive although it incorporates an archive. It is a logical and structured system to collect data which are subsequently entered into the computer, checked and stored and where also data may be compared, associated, related and combined to provide information in a form suitable to users. A system may also be seen as the integration of the user and the machine.

The planning, design and management of water services for domestic, industrial, agricultural and power uses and protection from the vagaries of floods and droughts, requires information on storages and fluxes in water for safe and economic design and operation. The need is growing with a growing population.

The activities under HIS can be broadly classified in the following categories:
 

• Assessing the needs of users

• Establishment of an observational network.

• Management of historical data.

• Data collection and transfer.

• Data processing analysis and reporting

• Data Exchange and reporting

• Data storage and dissemination