This engineering challenge has been designed to be fairly open-ended, and engages participants to design and build an instrument that can be used to measure rainfall. The activity uses easily available materials, and teaches participants about the need to have a calibrated system when designing and building a scientific instrument. There is a data collection capture sheet included with this activity. We have used this at large public outreach events, such as “Earth Day” , with groups of teachers in professional development workshops, with students in formal and informal education settings, and in STEM engagement events at libraries, museums, and schools.