For a limited time you can get the LifeStraw 1000 Liter Emergency Survival Water Purification Filter Drinking Tube from Altatac (via eBay) for only $14.95 + Free Shipping. The filter normally lists for $25, and Amazon is selling it for $20. The filter has received a super high 4.6/5 stars from over 1,000 reviewers at Amazon.