Put the limes, water, and sugar in a blender and pulse 3 to 4 times, just enough to extract the juice from the limes but not crush the skins (which would make the drink too bitter). Strain through a fi ne-mesh sieve into a pitcher. Taste and add more sugar if you like. Whisk in the chia seeds and refrigerate for at least 30 minutes, until completely chilled. Stir before serving, then serve over ice.