I found this about the Pre Mac SWP.

http://chppm-www.apgea.army.mil/WPD/WPDShare/177/AddInfo_PreMac_SWP.pdf

Apparently, according to this report, it is not effective for Giardia or Chryptosporidium.

Here is a good source of info for filters/purifiers, I think it may have been posted here before.

http://usachppm.apgea.army.mil/WPD/CompareDevices.aspx

I guess for now I'll stick with my MSR and Chlorine Dioxide tabs.

Thanks for the input all.

Blitz