WATER – THE UNIVERSAL SOLVENT
In its purest form, water is one of the most aggressive solvents known and will dissolve a material until the solution reaches saturation. Pure water is also a critical ingredient in many business ventures; manufacturing, power generation, health care, pharmaceuticals, research, food production and processing, etc. Each of these business sectors has a different but specific use for high puritywater. Water purity is relative to its use. Different industries have differentcritical levels or types of impurities; microelectronics – TOCs (totalorganic compounds); power – silica; pharmaceutical – bacteria; research –conductivity/resistivity.The specific purity needs, along with the analysis of the source water, formthe basis of treatment to produce high purity water.

While purity requirements are paramount, another critical selection criterion is the quantity. It would seem obvious that higher volumes of pure water are directly related to equipment selection, redundancy, and serviceability. For example, a system with low-volume demand might effectively accomplish some of the pretreatment filtration functions using cartridge-type filters and closed-loop piping distribution with little or no storage. At the other end of the spectrum, where pure water is fundamental to the process or where extremely high volume demands are normal, a system may be developed with redundant vessels, filters, and pumps to allow for service and/or replacement of components without interrupting either the production or purification processes.

While both the range of purity and the systems for producing high purity water vary widely, there are several fundamental concepts that should apply to all levels of systems. These fundamentals are areas where a deeper understanding by the owner/user can help the pure water system designer develop a systemthat is both efficient and economical for the selected project.

PRETREATMENT
Long lasting, high-performance water systems require appropriate process selection and routine maintenance. Generally, the process selection begins with a reviewof the pretreatment systems. Pretreatment allows each device or piece of process equipment to operate within its normal parameters. For example, a properly sized and installed particulate filter will protect the very fine openings of reverse osmosis (RO) membranes from becoming prematurely clogged with either ordinary par-ticulates or very large sized impurities, prolonging the life of the expensive membrane material while letting the “low-tech” filter do the heavy lifting. Neglecting the concept of progressive filtration is a common error made by those who are unfamiliar with the processes. Once through, one-size-fits-all approaches are destined for higher cost operation,early failure, and unreliable purity levels.