Setup your own home security systems offered by many agencies in Karachi otherwise security wise naval colony and Askari 4 good. Sure about no water problem in Askari 4 but don't know about Naval Colony. Most suitable areas for you is Tariq Road, PECHS, KMCHS, Bahadurabad and surrounding areas (very near to Tariq Road/Tower). water problem there not much but have problem. Askari 4 cost you 22 to 25 mil for 500 yds and 300-350 yards in Naval Colony. Askari 4 away from your desired areas also one road to Karsaz is open in clash times. Dalmiya road most of time disturbed by Shanti Nagar.
One more area you should consider is opposite of Islamia College and surrounding of Mazar-e-Quaid.There are mostly large houses (very expensive from 100 to 150 mil) but peoples started to divided in small parts and sell it hope you find some in your range.No water problem, better security,right in heart of city both tower and Tariq Road very near to it.