If your immune system is low and your body fights off the infection, you can get stomachaches after drinking water. Your body is trying to fight off something. So if you notice you got a stomachache after drinking water, then it could be that you might be starting to get cold. You might be getting sick. Maybe your allergies are acting up. It could be anything. Sometimes a hot water pack will help you to avoid this pain. You need to follow these drinking water rules: 1. Do not drink more than about a liter at a time. If you drink two liters at a time, that's too much, and you will get a stomach ache. 2. Use a hot water pack to stop stomach pain quickly. 3. Drink slightly hot water to help your digestion.