In a blender, blend 450g of the strawberries with the sugar, lime juice, salt, mint, if using, ginger, if using, and 2 cups (500ml) cold water until smooth. Press the strawberry mixture through a fine-mesh strainer into a large bowl or pitcher. Discard solids. Stir another 1 cup (250ml) cold water into the strawberry mixture.
Thinly slice the remaining 50g strawberries. Fill glasses with ice, mounding well above rims. Pour strawberry water over the ice. Garnish with sliced strawberries and serve immediately.