Combine the rum, lime juice, and simple syrup in a cocktail shaker filled with ice. Shake and strain into a collins glass filled with ice. Top up with seltzer water and garnish with a lime slice if desired.
Simple and easy, the Ron Collins is the Tom Collins' island loving brother. Instead of gin and lemon, the Ron Collins uses rum and lime for maximum refreshment.
I like using a nice light rum such as El Dorado 3 year, you want something will a little flavor but nothing too overwhelming. Don't cheap out too much on your booze, but there's no need to break the bank either.