During an emergency, the ability to purify water could be critical. This improved brick rocket stove could be built for about $10, if you have to buy the materials. It’s possible to salvage all of them. This is an improved design from the previous SurvivalCommonSense rocket stove post that has received nearly one million views.
You use any biomass stove at your own risk, since a variety of unfoerseen circumstances and/or materials could affect the safety of the stove.