Both the Pentek P-250 and Pentek P-250A are very effective drinking water filter sets. There is one difference between the Pentek P-250 drinking water filter set and the Pentek P-250A drinking water filter set, the Pentek P-250A reduces the contaminant called MTBE.
If you are not sure if you need to be concerned about MTBE in your water check with your local City Hall. Each city is required to test their water and make the results public. They will be able to tell you if there is any concern about MTBE.
If you have a private water source, like a well, you should have your water tested for MTBE and other dangerous contaminants.
If you know that MTBE is not a concern in your drinking water than you can purchase the Pentek P-250 Drinking Water Filter. The P-250 Pentek Water Filter can be found here:
http://www.waterfilters.net/culligan...ntek-P-250.htm
If you are not certain that you do not have MTBE is your water of you know that it is in your drinking water than you need to purchase the Pentek P-250A Drinking Water Filter. The P-250A Pentek Water Filter can be found here:
http://www.waterfilters.net/culligan...tek-P-250a.htm
The P-250 and the P-250A are interchangeable. If you have used one in you drinking water filters system than you will be able to use the other with no problems.