One of the big failures of mother backpacking technology, in my opinion, has been the inability to develop a lightweight portable water filter. For people interested in saving weight, chemical treatment has been the solution, but such a purification process can be time consuming, and will not always give you good drinking water.
Recently the portable, straw filters such as Aqua Mira Frontier Pro have exploded onto the market mainly because of their portability. An Aqua Mira Frontier Pro weighs only 2oz, making it a very appealing choice. These filters however have a huge down side, which is very often completely ignored. The problem is that they filter only down to 2 or 3 microns. Most good quality filters on the market filter down to 0.2 or 0.3 microns. A 3 micron filter will remove most parasites such as Cryptosporidium and Giardia, but will do absolutely nothing against bacteria such as E.coli, Salmonella, Cholera and Dysentery. This is a very large difference in filtering capacity. The decimal point is very important.
The downside with all these filters is the speed of pumping/filtering. They are somewhat slower than your standard backpacking water filter such as MSR Miniworks EX. On the up side, they are much, much lighter. If you are trying to save weight, and are thinking of going to an Aqua Mira Frontier filter, have a second look. There are lightweight filters out there that offer much better protection from contaminants, although probably at the cost of slower speed. Also remember, no filter is effective against viruses. They are rare in the Northern US, but if you are in an area where you think there might be viral contamination, make sure to take additional steps.