Apparatus (2) for sensing at least one parameter in water, which apparatus (2) comprises: (i) a conductivity sensor (6) for sensing conductivity in water; (ii) the conductivity sensor (6) is an electrode-based conductivity sensor having bare electrodes (12) which contact the water; (iii) there are at least four of the electrodes (12); (iv) the conductivity sensor (6) is fabricated on a substrate (14) using photolithography and etching; (v) the conductivity sensor (6) is an open cell sensor having a physically unconstrained electric field; (vi) the conductivity sensor (6) is of a dot construction comprising a dot and a surrounding formation; (vii) the conductivity sensor (6) has two electrodes which are for current stimulation and which geometrically bound and enclose another two electrodes which are for voltage sensing; and (viii) the conductivity sensor (6) is a laminar construction on the substrate (14).