Make your simple syrup by combining 1 cup water with 1 cup sugar. Heat the mixture just until all sugar is melted (no granules remain) and liquid is cloudy-clear, Doing let it boil (you will lose some via evaporation and allow the mixture to contain more sugar).Allow mixture to cool to room temp, then store in fridge is a sealed jar for up to 3 weeks. This should yield between 1½ cups and 1¾ cups...so 22 TBS worth.When ready to assemble coolers, first you want to supreme the limes. Like I described above. Once you have your limes cut into segments, place 2-3 segments in each glass and muddle them (with a muddler or wooden spoon). Get them all broken down, so you have pulp floating around your cocktail, yum!Fill the glass with as much ice as you like, then vodka, then 1½-3 TBS simple syrup (depends on the size glass you use and your preference for sweet).Top with seltzer, garnish with a lime slice and maybe a few thin shards of lime skin in the glass and enjoy!!