Some interesting links:
TWSA, Transparent Watercolor Society of America, www.watercolors.org
NWS, National Watercolor Society, www.nationalwatercolorsociety.org
WW, Warecolor West, www.watercolorwest.org
CSPWC, Canadian Society of Painters in Watercolour, www.cspwc.ca
LWS, Louisiana Watercolor Society, www.louisianawatercolorsociety.org
PWS, Pennsylvania Watercolor Society, www.pawcs.com