Add the sugar and water into a saucepan.

Place over a medium heat and stir until the sugar has disolved.

Once the sugar is dissolved, remove from the heat and let the sugar syrup cool.

Place the strawberries in a blender and blitz to a purée.

Add the strawberry purée into a large jug with the sugar water and add the lemon juice.

Combine well.

Pour into glasses filled with ice.

As far as I can tell, this will keep for a day chilled.  It has never lasted that long!