What, Why & Who


The Rain Harvest Calculator is a free online app that allows you, the user to evaluate rainwater harvesting potential. It picks up where most rainwater calculators leave off in that it allows you to plot the annual trend of rainfall in monthly increments so that you can see the trend and make better decisions regarding collection and tank capacity.


I built the tool because we (my wife and I) needed a better way of determining the rainwater havesting potential of prospective building sites. After building a complex (and cool) Excel spreadsheet to do the task I decided that creating a online tool would be a great way of both making it more portable for us and sharing it with others that might find it helpful.


I'm a software engineer and an outdoor enthusiast. I love building projects and figuring out practical solutions to everyday problems. We are currently dreaming about planning on building an off grid home. Feel free to send me feedback and comments. I love to hear from others that are using this tool.

- Darrel Stone