Sometimes water can slow the first stage of labour down. If you feel that may be happening, you can get out of the pool again. There is no rule saying you must stay in the pool once you are in it! In fact, it can be beneficial to get in and out of the pool to help the baby move down well into your pelvis, and to facilitate trying different positions.
Some women and birthing people find that the water makes them too hot during labour so they want to get back out again. There is debate about the best temperature for birth pool water to be at but generally, a comfortable temperature for you is best while you are labouring. It is important that you can easily raise your body up out of the water as that is how we lose heat while in water.
Using a pool may increase your chance of having a minor tear (or it may not), but it decreases your chance of having a severe tear or episiotomy. You can read more about the evidence around waterbirth on Evidence Based Birth.