A method of washing fabric articles in a tunnel washer that includes moving the fabric articles from the intake of the washer to the discharge of the washer and through multiple modules or sectors. Liquid can be counter flowed in the washer interior along a flow path that is generally opposite the direction of travel of the fabric articles in order to rinse the fabric articles. While counterflow rinsing, the flow rate can be maintained at a selected flow rate or flow pressure head. One or more booster pumps can optionally be employed to maintain constant counterflow rinsing flow rate or constant counterflow rinsing pressure head. A source of fresh, make-up water can be provided to adjust conductivity. Conductivity is monitored in at least one of the modules. Conductivity of fluid in the discharged fabric articles is monitored. Make up water is added to one or more modules before if the conductivity of water in the discharged fabric articles exceeds a threshold value. In one embodiment, one of the modules is an empty pocket that is drained of fluid when rinsing with counterflowing liquid.