Living conditions (New Delhi)

Hi everyone!
My friend and I are in the process of relocation to New Delhi because of job offer.
And now we are thinking about the best place for living in New Delhi. As I understand, a lot of foreigners live in South Delhi, is it true? We were initially thinking about Hauz Khas, Green Park, but our colleague lives in Dwarka and recommends this place. Could you please compare Dwarka with South Delhi?
And the most worrying question is about water. I know that water pollution is a problem in ND. Does the quality of water vary in different districts? Are there any neighborhoods, where water quality is better? E.g. Dwarka vs. South Delhi vs. Gurgaon
Thanks in advance!
Regards, Ksenia