Bad smell from borewell water

Sir

I dug a borewell 750 feet in 2017. We are using the water continuously since then, unfortunately for the last two weeks a bad sulphur like smell is coming from the water. There is no change in colour. 

I live in Hyderabad Toli Chouwki area. I do not know what is causing this problem.

Can you please suggest any agency that can professionally handle this problem with minimum cost?

Thanks

Fareed Ahmed

8-1-21/105 Suryanagar Colony Toli Chowki Hyderabad 500008

Mob: 9885886094