I use a SweetWater Guardian purifier system. It works great - even for that nasty EastTexas water. It it fairly light - compared to most others. There are some lighter ones out there though - and may be better. But the SweetWater is all I have ever used and know about. I know PUR makes a good one - it is supposed to be even lighter than the SweetWater. I will look it up and post some links below for you.
SweetWater:
http://www.backpackreviews.com/sweet...fiersystem.htm
PUR:
http://www.purwaterfilter.com/hikguidpor.html
REI's list:
http://www.rei.com/online/store/Cate...goryId=4500461
And it is still recommended that you use iodine or chlorine solutions to purify the water. I strongly recommend it for the water along the Lone Star Trail. That is some nasty yellow water!!!