Of all things, the toyota previa's water pump is the one part that's easier to replace than on most other cars. Most cars require messing with the timing belt to remove the water pump, but not the Previa. It's a simple remove hoses, remove oil filter bracket, and unbolt the pump! Piece of cake!
Every other car I've changed the water pump on has been a royal pain compared to the Previa!

https://m.youtube.com/watch?v=mrUD2z_qM6U