In the context of ▶ diafiltration, wash water is simply another term for diluent. This is the water used to replace impure solvent while retaining the desired product. A typical example might be the washing of a cell suspension prior to cell disruption to release an intracellular product.The typical way of doing this would be to subject the cell suspension to batch crossflow microfiltration while adding wash water at a rate that exactly balances the filtrate (▶ permeate) flow rate. Thus, the cells are retained, but the impure liquid in which the cells are suspended is gradually displaced by wash water.