DD is just over 8months now and has been eating...

DD is just over 8months now and has been eating solids for 3 months. She currently has fruit puree for breakfast, lunch and dinner (although has savoury as well for lunch and dinner) I would like to start her on weetabix or porridge for breakfast so she is not having quite so much fruit, but should I mix it with water, milk or formula to make it runny?