Add rosemary sprigs to saucepan and lightly toast to open up aromas. 

Add water, sugar, then blackberries to the lowly heated saucepan. 

Lightly mash the blackberries with potato masher. 

Stir frequently on medium-low heat until the mix begins to boil and all the sugar is dissolved. 

Turn heat off and mash with potato masher one more to release juices and oils.  

Allow to sit and steep for half an hour or more. 

Strain through fine metal colander to storage container.