Fouling of a reverse osmosis membrane can seriously harm the ﬁltration system, ultimately reducing the life of the system while incurring added cleaning costs. A pretreatment system can help to not only extend the life of a reverse osmosis membrane, but ensure the ﬁltration system is operating at its designed efﬁciency. The best available technology for determining the fouling potential of a reverse osmosis system is by measuring the inlet’s Silt Density Index (SDI). SDI measurements need to be taken prior to designing an RO pre treatment system. Raw water SDI values, measured multiple times during a 60 day period, averaged just over 4. The ﬁltration challenge was clear!