Do the zinc soap bars lather?

This depends on the hardness of your tap water. The hardness of water is determined by the milligrams of calcium carbonateper litre and is reported it in parts-per-million or ppm. In general, water with less than 60ppm is soft. Water 60-120ppm is moderately hard.  Water with greater than 120ppm is hard.  The zinc bars lather good until 140ppm.