Locate the two water pipes that connect to the softener. One carries the water into the tank; the other carries it out. Located near the softener is a third pipe that runs between the inflow and outflow pipes and connects them to each other. It has a knob on one end.
Push the knob in towards the pipes to stop the flow of water into the softener. If you do not have a valve with a knob as described, proceed to step 3.
Look for a pipe running between the inlet and outlet pipes that has a handle in the center. Twist the handle on the valve bypass counterclockwise to open the bypass. Between it and the softener, the inlet and outlet pipes also have handles to control water flow. Shut them by twisting the handles clockwise. Water will now flow through the open bypass pipe, not into the water softener. If you have no valve bypass, proceed to step 4.
Look on the tank for a button on the side or near the top labeled "Water Bypass" or something similar, and follow any instructions it might give. If you find no water bypass, proceed to step 5.
Shut off the main water supply to the house to stop the flow of water into the softener tank.