Fresh water deficiency caused by climate change calls for employing novel measures to ensure safety of drinking water supply. Wireless sensor networks can be used for monitoring hydrological conditions across wide area, allowing flow forecasting and early detection of pollutants. While there are no fundamental technological obstacles to implementation of large area sensor networks, their feasibility is constrained by unit cost of sensing nodes. This paper describes a low-cost pH sensor, intended for use in fresh water monitoring. The sensor was fabricated in a standard thick film process, and an off-the-shelf resistive paste was used as a sensing material. For the fabrication of sensor, RuO2 resistive paste was screen printed on the alumina substrate with silver conducting layer. Test solutions with pH ranging from 2 to 10 were prepared from HCl or KOH solutions. The potential difference between reference and sensing electrode (electromotive force emf of an electrochemical cell) should be proportional to the pH of a solution according to the Nernst equation. The fabricated sensor exhibits Nernstian response to pH. Influence of storage conditions on sensing performance was also investigated.