The Lishtot TestDrop Pro device cannot reliably indicate microbial water safety

Low-cost, scalable tests hold great potential to increase the availability of water safety data globally, especially in resource-limited settings. We evaluated the Lishtot TestDrop Pro, a commercially available, low-cost triboelectric-based sensor marketed for real-time determination of water contamination, including microbiological safety. We prepared a total of 199 water samples by serial dilution of raw wastewater influent into deionized water to produce a range of E. coli counts from <1 to too numerous to count (TNTC, > 300 per dilution plate) CFU/100 mL to evaluate the sensor. We tested these waters using the manufacturer’s instructions. We collected sensor readings using three settings on each of five devices, generating nearly 8,955 individual measurements to compare against E. coli measured via standard membrane filtration assays (EPA Method 1604), a common metric of drinking water safety. We found no statistical correlation between the sensor score and E. coli presence in water: 43% of sensor readings indicated “safe” when wastewater and E. coli was present, and 56% of samples lacking E. coli were deemed “unsafe” by the sensor when wastewater was absent. The Lishtot TestDrop Pro is not an accurate method for measuring microbiological water safety.