Investigation: Rainwater Cistern Sizing
This investigation attempts to solve two problems simultaneously. The first is how can a cistern be sized using specific, historic rainfall data rather than long-term averages. The second is how can a calculation tool be best packaged and distributed for widespread use.
April 17, 2025 | Posted by Corey Squire
Introduction
Two trends over the past few decades should cause us to rethink the way we use weather data for design. The first trend is climate change. The second trend is big data. Averages were developed as a way to reduce error in relatively small data sets. Today, with huge quantities of easily accessible data and inexpensive ways of manipulating it, averages might be on its way out in favor of precise, actual metrics.
The Tool
The cistern sizer takes three metrics into account: The size of the cistern, the daily water demand, and the size of the catchment area. It uses daily rainwater data from the previous 30 years. For each day in the data set, the tool calculates the net water projected to enter or leave the cistern, keeping the minimum as zero and the maximum as the size of the cistern.