How can I persist data from a source in PowerBI

Hello, 

I am getting data through an API source and need the data in its granular form, but also in form of aggregated tables.

Whenever I reference a previous data source ( Source = datasource )  PowerBI seems to go back to the original data source rather than grabbing the data out of memory. 

Is there a way to control how often PowerBI actually goes to the source, and can I persist data in the product?

Thanks, V.