Presently, monitoring membrane integrity is carried out in one of two ways. Thefirst is to try and measure a property inherent to the membrane in an attempt todiagnose its integrity. The second is to measure the quality of the permeatewater and to use that as an indicator of membrane integrity. The primary means ofmeasuring the membrane directly is the pressure decay test (PDT). The membrane isdrained, and then, either the feed, or the permeate side is pressurized with air.The rate of pressure decay under conditions of a compromised membrane is greaterthan when the membrane is intact. There are however, a few problems with thistechnique. It requires a membrane rack to be taken off line and therefore thefrequency of integrity testing is severely limited by practicality. Also, certainmembranes will experience some pressure decay, even when the membrane is known tonot suffer from integrity issues. Measuring the particle content of permeatewater is done using turbidimeters, laser turbidimeters and particle counters.Typically, one turbidimeter (or a laser turbidimeter) and one particle counter(>2 microns) are employed to monitor the quality of the permeate from each rack.Reports in the literature suggest that both the laser turbidimeter and theparticle counter are capable of detecting a break in one fiber out of about 5000(as is the case in a single cartridge pilot system). However, the dilution effectfrom one compromised fiber out of 250,000 (as would be the case in a full-scalerack) would render their sensitivity insufficient. This difficulty could, inprinciple, be overcome in one of two ways: by significantly increasing thesensitivity of the monitoring instruments or by monitoring multiple points(ideally on every membrane module). Increasing the instrument sensitivity isproblematic because of the added burden of maintaining such an instrument. Forexample, the ultra-pure water industry routinely uses particle counters capableof counting particles down to 0.05m. Instruments such as these require sampledelivery channels as small as 50m, which can easily be clogged. Additionally thecosts are extremely high. The instrument we report on in this paper takes theapproach of using multiple sensors of adequate sensitivity deployed on eachmodule of a membrane filtration system. Includes figures.