In a small saucepan over low heat, combine water, sugar, and strawberries. Let cook, stirring occasionally, for about 15 minutes or until strawberries are soft.
Strain simple syrup into a bowl and discard strawberries (or save them to put on your oatmeal, pancakes, etc.!). Once no longer hot, pour into a jar and keep in the fridge.
To assemble the cocktail, fill two pint glasses with ice all the way to the top.
Pour two ounces of rum into each glass, followed by 1 ounce of strawberry simple syrup into each and the juice of one lime into each. Fill to the top with Lime LaCroix and stir with a straw to combine.
Garnish glasses with extra strawberries and sliced limes if desired.