A membrane surface monitoring cell for use in monitoring membrane scaling, particulate fouling, organics, and biofouling configured for receiving a feed stream and discharging a concentrate stream, the membrane surface monitoring cell comprising: a) a visually-observable membrane having a first surface on an active feed-side; b) a retentate module having: (i) a retentate module support block, (ii) an optical window within the retentate module block, the optical window for viewing the visually-observable membrane, (iii) an inlet conduit for a feed intake stream into the membrane surface monitoring cell, (iv) an outlet conduit for outlet of a liquid concentrate stream; and, c) a permeate module having: (i) a permeate module support block (ii) and a permeate outlet conduit to channel permeate away from the permeate module; characterised in that the membrane surface monitoring cell further comprises d) an edge-lit light guide having an aperture forming a retentate channel operable to isolate pressurized fluid in the retentate channel, the visually-observable membrane positioned adjacent the edge-lit light guide and positioned to overlay the aperture, wherein the edge-lit light guide is composed of a transparent or translucent material to illuminate the first surface of the visually-observable membrane, thereby allowing an observer to view scaling, particulates, and biofouling on the first surface of the visually observable membrane; e) an edge illumination light source (18, 50, 62) affixed to the edge-lit light guide, the edge illumination light source operable to illuminate the edge-lit light guide, thereby providing illumination substantially parallel to the visually-observable membrane; wherein the edge-lit light guide is configured to be positioned between the retentate module and the permeate module; and the permeate module further having a permeate collector to receive permeate that has passed through the aperture of the edge-lit light guide and visually-observable membrane. a) a visually-observable membrane having a first surface on an active feed-side; b) a retentate module having: (i) a retentate module support block, (ii) an optical window within the retentate module block, the optical window for viewing the visually-observable membrane, (iii) an inlet conduit for a feed intake stream into the membrane surface monitoring cell, (iv) an outlet conduit for outlet of a liquid concentrate stream; and, (i) a retentate module support block, (ii) an optical window within the retentate module block, the optical window for viewing the visually-observable membrane, (iii) an inlet conduit for a feed intake stream into the membrane surface monitoring cell, (iv) an outlet conduit for outlet of a liquid concentrate stream; and, c) a permeate module having: (i) a permeate module support block (ii) and a permeate outlet conduit to channel permeate away from the permeate module; characterised in that the membrane surface monitoring cell further comprises (i) a permeate module support block (ii) and a permeate outlet conduit to channel permeate away from the permeate module; d) an edge-lit light guide having an aperture forming a retentate channel operable to isolate pressurized fluid in the retentate channel, the visually-observable membrane positioned adjacent the edge-lit light guide and positioned to overlay the aperture, wherein the edge-lit light guide is composed of a transparent or translucent material to illuminate the first surface of the visually-observable membrane, thereby allowing an observer to view scaling, particulates, and biofouling on the first surface of the visually observable membrane; e) an edge illumination light source (18, 50, 62) affixed to the edge-lit light guide, the edge illumination light source operable to illuminate the edge-lit light guide, thereby providing illumination substantially parallel to the visually-observable membrane; wherein the edge-lit light guide is configured to be positioned between the retentate module and the permeate module; and the permeate module further having a permeate collector to receive permeate that has passed through the aperture of the edge-lit light guide and visually-observable membrane.