This dataset reports total arsenic (AsTot) results analyzed using an in-field biosensor system, Field-Ready Electrochemical Detector for Arsenic (FRED-Arsenic), developed by FREDsense Technologies Corp., Calgary, Alberta, Canada. Samples were collected from two public-supply wells (NH-SGW 93 and NH-SGW 65) and one private well (NH-KFW 87). NH-SGW 93 and NH-KFW 87 both withdraw water from a crystalline-rock aquifer. NH-SGW 65 withdraws water from a glacial sand and gravel aquifer. Twelve samples for NH-KFW 87 were collected and analyzed on May 14, 2019 with sample times ranging from 0730 to 1800, and 12 samples were collected and analyzed on August 20, 2019 with sample times ranging from 0830 to 1320. Eleven samples for NH-SGW 93 were collected and analyzed on May 15, 2019 with sample times ranging from 0838 to 1437, with the last sample collected when the pump was turned off; 12 sampled were collected and analyzed on August 21, 2019 with sample times ranging from 0807 to 1159. Twelve samples for NH-SGW 65 were collected and analyzed on May 16, 2019 with sample times ranging from 0931 to 1400; 12 samples were collected and analyzed on August 22, 2019 with sample times ranging from 0813 to 1057.