Our complete line of Type I water purification systems includes systems that will produce basic Type I Analytical Grade water up to and including Type I Ultralow TOC (2-5ppb) Biological Grade Water that is RNase, DNase, pyrogen and endotoxin free.  The models are as follows:  2001A, 2002A, 2002AL, 2001B, 2002B, 2002BL.  In addition, a UV Sterilizer can be added any of the models mentioned.  This will help prevent the uncontrolled growth of microorganisms within the system.  Please notice that ALL systems with a "e;2"e; in the model number indicate that they include 2 DI modules.  This means the ion exchange capacity of the system 4,000 grains.  The amount of ion exchange capacity of ALL water purification systems is directly related to how much ultrapure water the system will produce before exhausting itself.  In other words, the higher the capacity, the longer the kit will last.  The models with a "e;2"e; in it can also accept ordinary tap water, if the TDS (totally dissolved solids) level is no higher than about 170 ppm)