Using harvested rainwater is a popular frugal tactic for obvious reasons: rainwater is free, easy to collect, and abundant. However, it is always a good idea to filter rainwater first since it may have harmful contaminants. No need to fork out cash for an expensive commercial system though. Instead, check out this cool tutorial on Instructables.com for a homemade water treatment train. While it is not recommended for drinking or cooking, you can use the filtered water for gardening and cleaning. Click the link below and start building.