Texas Instruments (TI) has found that developing “water balance” diagrams that map water inflows, outflows and intermediate reuse between production and support areas in a manufacturing plant provide valuable information for improving water management and reducing costs. A water balance is very beneficial during the design of manufacturing plants as well as during efforts to optimize subsequent plant operations, particularly where appropriate flow meters are installed. Identifying the amount and quality of water needed in all (or major) water use areas allows the development of a better-integrated water use program during process design that may reduce demand for freshwater. A water management system can also match water use requirements with other water streams in the facility of appropriate quality, enabling reuse without additional treatment.

TI’s semiconductor fabrication plant in Miho, Japan has been in operation since the early 1980s as a zero industrial wastewater effluent plant. The plant was built this way at the request of the local neighbors and government. At the time, the area lacked the infrastructure to support a more conventional plant design, which typically uses over a million gallons of water per day. The production area at the Miho plant reuses process water over and over again, enabling the plant to consume a much smaller amount of water than comparable semiconductor plants. Some generated production “byproducts” are segregated from process water and collected for reuse as raw materials at other companies or disposed of as concentrated waste solutions.

The Miho plant has found water balances to be useful tools for improving process designs and communicating about water use. A sample water balance for the Miho plant is shown below.

Miho Water Balance

The complexity of a water balance depends on the type of facility and the characteristics of the local area. A site with only a few water use requirements might need only a simple water balance prior to starting a water management program. For a complex site with many water uses, an accurate site water balance should consider seasonal impacts as well as water use at various production rates. For example, at the Miho plant, and a similar plant in Hiji, Japan, there are actually many water pipeline interconnections between areas to minimize water use. Many of these connections at the Miho and Hiji plants are measured on varying frequencies to assure gains are being maintained and to identify additional opportunities.

Using an accurate water balance in a sound water management program can improve:

• Identification of current and future water uses
• Consideration of water conservation opportunities during the plant design phase
• Ability to troubleshoot problems during actual plant operation by using flow meters to compare actual water use with plant design
• Identification of water reuse opportunities during plant expansions
• Identification of other future cost-effective water conservation projects
• Ability to communicate water use issues within the company and to external critical customers