The quantity of water needed depends on the design of the production plant and whether or not it is built in conjunction with a feedlot. Modern technology and design can substantially reduce the amount of fresh water needed by a stand-alone ethanol plant. There are "zero discharge" plants in operation that recycle virtually all of the water used in production, limiting the need for large supplies.
Most plants are designed with "in-house" water treatment systems for supply and discharge.
There are two water uses in a typical ethanol plant. The first is for liquefaction of the feedstock. Water must be clean and treated so there is no microbiological contamination. The quality level depends on plant design.
The second is non contact water, primarily used for cooling. This may be recycled cooling tower, well or river water. In the latter case water is returned to a river or lake.
There are "zero discharge" plants in operation. Most plants that do discharge process water should not have a biological oxygen demand (BOD) value higher than domestic sewage (300 to 400). This water can/should be treated in the plant.
Sodium hydroxide is used as a cleaning agent and is also treatable using in-plant treatment systems.