Is frequent thirst of water a necessary symptom of diabetes? could you have diabetes even if you don't have that symptom?

Yes: Many people with diabetes have no symptoms at all. Symptoms related to diabetes occur when sugars are very high (over 200 mg/dl). As sugars go high, more sugar goes out in the urine causing increased urination. As you urinate more you get thirsty and drink more. But if sugars are under 200 you may have no symptoms and yet those high sugars can cause long term problems.