A buffalo grass lawn will go dormant (brown) after the first cold spells/frosts in October, after which you can discontinue watering. Part of the reason for buffalo grass's low annual water need is that it is a warm-season grass that goes dormant earlier in fall and greens up later in spring than cool-season grasses like bluegrass.
A bluegrass or buffalo grass lawn could benefit from watering during extended winter warm/dry spells; use a hose and sprinkler to apply the water. Avoid excessive winter watering of a buffalo grass lawn so you don't promote the growth of cool-season weeds. Cool-season lawns like bluegrass receive the most benefit from winter watering.
See also:Fall and Winter Watering
and Buffalograss Lawns