Water Usage Calculator

This week I’ve been studying water usage to determine rain water collection tank sizing. Texas A&M Agrilife Extension has a useful rainwater harvesting calculator. Plugging in roof water catchment area (in my case 870 square feet for the main building and porch roofs), monthly average rainfall amounts, rain water collection tank size and monthly water usage amount the calculator generates a report showing how your system would perform over the course of three years. The report shows how much water you’ll have stored each month and when and how much supplemental water you’ll need each month. You can also simulate drought conditions in some years by reducing average rainfall amounts by a percentage.

At 80% of annual rainfall, no supplemental water was required with a 2000 gallon tank and a monthly usage amount of 1125 gallons. I created a calculator to determine what using a 1125 gallons for two people looked like. 

I’m planning to use a composting toilet so there’s no category for toilet water usage. The 4 minute shower length might be a little austere but it seems doable. The shower head flow rate really matters. Changing to a really low flow head that delivers 1.6 gallons per minute would increase average shower length to 5 minutes.