If your tent is leaking, it's probably because the seams aren't sealed properly or the fabric itself is damaged. However, if you're noticing water on the inside of your tent, it's likely condensation. Condensation happens when warm air hits cooler surfaces, such as the walls of your tent. It can be more pronounced in humid conditions or if you're using a lot of body heat to keep warm. To reduce condensation, open vents and windows when possible and avoid cooking inside your tent. If you have a waterproof fly, make sure it's not touching the inner walls of your tent, as this will create a barrier that won't allow moisture to escape.