In the field of water quality monitoring, there is an increasing demand for compact, low cost multiparameter water monitoring probes. The goal of the H2020 Proteus project (www.proteus-sensor.eu) is to meet this demand: based on the use of a set of novel conjugated polymers (FR1753131) functionalizing non-covalently multi-walled carbon nanotubes, we herein demonstrate the simultaneous monitoring of pH, chlorine, chloride and calcium ions with a single heavily minaturized sensor chip. The principle of sensing is based on the resistance variations of the functionnalized carbon nanotube network (deposited by ink-jet printing) upon changing chemical concentrations in water. In this paper, we present the functionalization strategy, from polymer design to proof of CNT functionnalization to CNT-polymer interaction modeling. Then we show the fabrication process and study the sensor array response, both in the lab and along field deployments. The measurements clearly show selectivity between the different CNT-polymers sensors, for instance pH sensitivity enhancement by a factor of 10 compared with the other devices with one of our polymers tuned with a urea-derivative. For field testing, the sensor chips are integrated into a 250cm3 pre-industrial sensor nodes and tested for several weeks in Sense-City 40m water loop. We demonstrate the first scale one deployment of arrayed carbon nanotubes chemical sensors, for instance showing demonstrating the capability to monitor active chlorine (HClO) or pH in real time in the field.