“Personal” water filters are small and intended for lower-volume uses such as hiking, backpacking, and emergency kits. These filters are effective, small, inexpensive ($30 or less), and generally remove impurities as small as 0.1 – 0.2 microns. You can drink directly from the filter. This level of filtering is sufficient for water found in most lakes and waterways. Extremely contaminated water requires both filtering and then a secondary treatment using chemicals or a UV to kill the micro-fine bacteria and viruses. These are some of my favorites.
The Sawyer Mini (review) is my personal favorite because it can connect to a standard water bottle, water bladder (included), or hydration pack (inline). It filters up to 100,000 gallons, filters to 0.1 microns, is available in a variety of colors (to distinguish filters), costs about $25, and is easily cleaned by backflush. Every hiking and vehicle kit should include a Sawyer Mini or Squeeze filter. The Mini is simple, lightweight, effective, and inexpensive.
The Sawyer Squeeze (review) is the big brother of the Mini. It connects to a water bottle, bladder (included), or can be connected inline on a hydration pack. The Squeeze is slightly larger than the Mini and can filter a greater volume of water more quickly. The Squeeze Personal Kit sells for about $40 and includes the filter, backflush syringe, bladder, and straw. The All-in-One Squeeze kit (about $60) includes the Personal Kit plus bucket fittings (including a spade bit to drill the hole). With the bucket kit you can use the Squeeze as a higher volume gravity filter. Water added to the bucket flows through the Squeeze to a container with the filtered water.
The Lifestraw looks like a very fat straw. You insert the Lifestraw into a water source and drink directly from it. The Lifestraw is small, inexpensive (about $20 retail), filters down to 0.2 microns, and will filter about 1,000 liters (264 gallons) of water. This level of filtering is sufficient for most reasonably clean water sources and it removes the majority of microorganisms. I prefer the Sawyer Mini because it is almost the same cost (about $25 versus $20 for the Lifestraw), filters to 0.1 micron (Lifestraw is 0.2), lasts for 100,000 gallons (Life is 1,000 liters), and it can attach to a bottle or bladder. The Lifestraw is most definitely a good product but I think the Sawyer Mini is a bit better.
I think that every hiking and vehicle kit should include a personal water filter. You may never need it but it could save your life if you do need it. I think every hiking pack should include a Sawyer Mini or a Lifestraw. I personally prefer the Sawyer Mini because it will filter more water and it filters down to 0.1 microns. For a vehicle kit consider including the larger Sawyer Squeeze filter. The Squeeze allows you to purify a greater volume of water more quickly than the Mini. For less than $25 a personal filter is very cheap insurance to add to your kits.