Arsenic is a serious problem in groundwater in Bangladesh, West Bengal, and other regions, with up to 100 million people worldwide estimated to be at risk. Long term consumption leads to arsenicosis, skin lesions and cancers. There is a clear need for cheap, simple, non-toxic field test kits for routine monitoring of arsenic levels in drinking water. Whole-cell biosensors may provide a solution, but current systems require expensive reagents or laboratory equipment. Here we present two new approaches: firstly, a biosensor in which detection of arsenic is signalled as an easily detectable drop in pH; secondly, a chromogenic system using endospores, which can be stored and distributed in dried form without requiring freeze-drying or refrigeration. Further development of these concepts may lead to a cheap practical device which can be used in the field by workers with minimal training.