Levels Explained

Published in Water Filtration
Written by Nicholas Papp

Creation Date Wednesday, 20 April 2011.

Each discipline specifies several other criteria for each Type (i.e., I, II, III, or IV). Needless to say, the three disciplines do not agree on exactly what constitutes each type.

For practical purposes:

  • Type I ultrapure water usually means water that has 18 Megohm-cm or greater specific resistance, with other attributes such as bacterial count, TOC (total organic carbon), pyrogen and/or endotoxin and/or R-Nase and/or D-Nase levels, and specific ionic contaminant levels usually specified by the end user. It is essentially a given that this water meets the other criteria specified by CAP, ASTM and NCCLS.
  • Type II water usually means water that has 1-2 Megohm-cm or greater specific resistance, with other attributes such as bacterial count, usually specified by the end user. It is essentially a given that this water meets the other criteria specified by CAP, ASTM and NCCLS.
  • Type III water, per the CAP and NCCLS, means water that has 0.1 Megohm-cm or greater specific resistance, while ASTM defines it as having 4 Megohm-cm or greater specific resistance!
  • Type IV water is only defined by ASTM, as having 0.2 Megohm-cm or greater specific resistance.

About the Author

Nicholas Papp

Nicholas Papp

Nicholas Papp has a B.S. in Physics, with Minors in Chemistry and Math, from Baldwin-Wallace College. He is the Vice President and General Manager of AQUA SOLUTIONS, INC., and has worked in the water filtration/purification industry for more than 35 years.