If you have interest in this field then you should go for it but first consider below points -

There are numerous career opportunities available for hydrologists in India as well as in abroad also.  Numerous research institutions in addition to oil and gas industries take in students of hydrology. For M.TECH students chances are decent for the same. One other job option available for hydrologists is to work in the fields of education. Those who have a NET or PhD can get employed as Lecturers or Assistant professors with institutions that teach hydrology and geosciences. The remuneration for this field is good too.

Hope this helps!!!

Good Luck!!!