Abstract: A disclosed fluid purity monitoring system employs a network of preferably information-transmissive cables fixed in place within a body of fluid. Sensors sensitive to fluid impurities are supported at various places on the network. Data representative of impurity levels transmits to a collection point via the same cables at which the sensors are supported. One system employs at least two pluralities of sensors sensitive to different fluid impurities. Another system employs electrically conductive cables fixed in place substantially in a common plane, with some cables oriented substantially parallel to each other and intersecting other cables. In that system, the data transmits to the collection point via a separate electrical circuit for each one of the sensors. Each circuit includes a series connection of the pair of cables that intersect proximate to the sensor's support point on the network. Advantageous variations and methods are also disclosed.