This is true because the water would have gravitational potential energy that is caused by the water being held back by the dam and the water wanting to flow down.
This can be converted into kinetic energy when given the chance to, such as having a turbine on the dam.
I don’t see the video but I can still answer number 2! One example is when you boil water it evaporates as it gets hot. Another example is when you take a shower, the water on your body evaporates as you dry!