Its not like that the Person wont drink water much only because he is cancer asc . there are many cancer asc who even wont drink enough water at all . its all depends on moon placements and most importantly janma nakshatra .
Your nakshatra says all being born in krittika person is very hot and impulsive . interestingly your sun is debli but he is aspecting lagna lord in full power that is the reason , another thing is aries is hot firey sign lagna lord placed in aries gave you thirsty feeling also mars denotes thirsty ness person who have mars in own house or exalted will have high level of thirst . and rahu pours fuel to it . so thats my conclusion as far as i know . also your moon is in last degree of aries so its literaly in taurus and taurus is aspected by mars so again its even perfect to say you have much thirst .