As you get older, your body's signals get weaker. When you are young, if you drink only when you are thirsty, you will probably get enough water. The problem continues to get worse as you get older. So after age 50 or so, you need to drink fluids even when you are not thirsty. This is particularly important if you have retired to an area of the country that is warmer than you are used to, such as California, Florida, or the Southwest.
Dehydration can cause serious problems in older adults.
Even mild dehydration may cause constipation as well as other problems. Have more soups at your meals. Drink more fluids when you've had vomiting or diarrhea. Keep a glass of water to drink while you are watching TV or relaxing. Drink plenty of extra fluids after getting even mild exercise.