Health benefits from point-of-use (POU) water treatment devices come only with consistent use. Embedded sensors can measure the consistency of POU-device use and can provide insights about improving it. We demonstrate both potentials with data from SmartSpouts: accelerometer-based sensors embedded in spigot handles that record the duration and timing of use. In the laboratory, most sensor readings correlated well (>0.98) with manually timed water withdrawals. In the field, SmartSpouts measured >60,000 water withdrawals across 232 households in Limpopo, South Africa. Sensors proved critical to understanding consistent use; surveys overestimated it by 53 percentage points. Sensor data showed when households use POU devices (evening peaks and delayed weekend routines) and user preferences (safe storage over filters). We demonstrate analytically and with data that (i) consistent use (e.g., 7 continuous days) is extremely sensitive to single-day use prevalence and (ii) use prevalence affects the performance of contact-time-based POU devices, exemplified with silver tablets. Deployed SmartSpouts had limitations, including memory overflows and confounding device relocation with water withdrawal. Nevertheless, SmartSpouts provided useful and objective data on the prevalence of single-day and consistent use. Considerably less expensive than alternatives, SmartSpouts enable an order of magnitude increase in how many POU-device sensors can be deployed.