My favorite water filter would be a lousy choice for a go bag if you had to evacuate on foot or were in a very crowded vehicle. There are lots of commercial water filters on the market. Some are very big and heavy and some are very small.There are some tiny ones available that are like a drinking straw and are very light and easy to carry. These do not filter very much water and the cost per gallon is high.
My personal preferences in filters may not work at all for someone else. They are largely a matter of what an individual likes and wants to spend and their circumstances. The most likely disasters in your area could also influence your decision on a water filter for emergency preparedness.
I will just tell you about them and you can decide or go read more about them and then decide what you want.
My favorite is a ceramic filter that has silver in the ceramic filter elements. You can buy these according to size of filter elements, and quantity of filter elements. They work by gravity. You pour the water to be filtered in the top. The water goes through the filter elements and into a lower container with a spigot that you can take drinking water out of. The bigger and more filter elements you have in this filter, the faster and more water you can filter. They are big and heavy and cost a lot. They are easy to use and you get very clean water from them. The per gallon cost is low and they filter a lot of water before you need a replacement filter element.
There are water filters that are made for filtering water for a whole village. They are made so that they can have water pumped by muscle power through a filter. This allows a lot of water to be filtered in a short while. These are good if you have a very large family or want to filter water for a village. They cost a lot, the cost per gallon is low and they are fast. They are not very portable.
There are little straw water filters that can be easily carried in a go bag or pocket for everyday preparedness. They are pretty cheap, but the cost per gallon is high.
Some water filters look like a sports water bottle. You put your water to be cleaned in the bottle and sip out of a straw. The clean water comes out of the straw. This is not too expensive, the cost per gallon is slightly lower than the straw types, but still high.
You can buy tablets or liquids to put in water and shake it up and let it sit for a while. They kill germs. They are cheap, and take very little room and are light and are easy to carry. Their cost per gallon is low. Their disadvantage is that you are drinking the stuff that killed the germs.
You can find some of these various types of filters, especially the smaller, lighter ones, in sporting goods and backpacking stores. Military surplus stores often have water filters.
The larger ones, like the ceramic element ones with silver in them, are harder to find. Companies that sell food storage and that specialize in emergency preparedness have them. Places that sell bulk foods and farm supply stores online and offline often have water filters, including the big ones.
The whole village ones can be found in places that sell to missionaries and to homesteaders.
I want to write about go bags next.