Most people drink close 5 to 6 glasses of water per day on an average. There are people who have tendency to drink more water, say 8-10 glasses per day. This is true under normal conditions.
If your profession involves physical labor it would be normal for you to be thirsty more often due to the continuous dehydration through perspiration.
If you eat food which is has salt in it, it is likely that you will feel thirsty when you are done with the meal. This is because the body requires water to flush out the salt deposits in the body.
It is not a necessity to drink water when you are not thirsty. It is an added strain on the kidney if you keep drinking water needlessly. You should drink water when you feel thirsty.
If you eat a diet rich in fruits it would provide your body with all the required water since fruits have close 80% water content. People who follow an all fruit diet hardly ever feel the need to drink water.
It would simple be because the body does not feel dehydrated. The body has a self sustaining mechanism. Whenever there is a lack of water, it would demand it through inducing thirst. When there is enough water in the body you will not feel any thirst.
Most people who stay in regions with a cold climate or have air conditioning usually don't feel thirsty often. This because there is no loss of water through perspiration and hence dehydration does not set in.
There is also a possibility that your diet is rich in fruits and low in salt. Since fruits satisfy body's need for water due to their rich water content, you will rarely feel thirsty.