Place nuts in a large bowl and add water tocover by 2".
Let stand at least 12 hours (thisis key for silky, nongritty results; the longerthe nuts soak, the smoother the milk will be).
Drain nuts; discard soaking liquid. Puréenuts, agave, salt, and 4 cups very hot water(but not boiling; hot water yields creamiermilk) in a blender on high speed until verysmooth, about 2 minutes. Strain througha fine-mesh sieve into a medium bowl,pressing down on solids; discard nut pulp.Thin nut milk with water as necessaryto reach desired consistency.
Transfer toairtight container and chill until cold.
DO AHEAD: Nuts can be soaked2 days ahead; cover. Nut milk can be made3 days ahead; keep chilled.
