HOT WATER by Don Wallace (Soho Press: $18.95; 298 pp.). Whatever happened to BMWs and country-club memberships as status symbols in Yuppiedom? What's this business of the husband going in for high-tech bass fishing--complete with 70-mile-an-hour boats, sonar equipment, depth meters and salinity read-outs, and the wife embracing war games complete with paint-filled bullets and all of the other Soldier of Fortune frills? Wacky or not, these are the Footes (Gar and Virginia Roy) of Valhalla, Miss., and they are not the Joneses from down the street. "Hot Water" manages to have some pretty funny situations built into it, including what happens to Gar when, as the local Coca Cola bottler, he openly revolts against the introduction of the ill-fated "New Coke." No big moral lessons here, but what the hay.