The data presented in this study are openly available within the manuscript and its Supporting Information Files. The quality assurance project plan (QAPP), the standard operating procedure (SOP), and the Arduino IDE program file related to the Mayfly version 1.0 data logger board will be available upon request.

Details on the summary of literature for prioritizing the contaminants of concerns related to roof rainwater harvesting; examples of QAQC equipment calibration or operational check log sheets; summary of the missing TEST sensor raw data; and statistical summary of the split clean data (Tables S1–S10). Research site location; low-cost sensors; data logger board; QAQC equipment; data cleaning approach; raw TEST sensor data compared with QAQC sensor data; logger box ambient condition data; and TEST sensors’ clean data along with the correlations among various combination of the three parameters (Figures S1–S8); additional reference.