Studies with a new tool - the Membrane Fouling Simulator (MFS) -illustrate that the MFS can be used to quantify and characterize fouling. Using the MFS, fouling can be monitored by (1) operational parameters like pressure drop, (2) non-destructive (visual, microscopic) observations using the sight glass and (3) analysis of coupons sampled from the membrane sheet in the MFS. The small scale of the MFS makes it easy to handle and requires small amounts of water and chemicals, enhancing the possibility to test several MFS units in parallel. A comparison study of the MFS and spiral-wound membrane modules showed the same fouling. The MFS is representative for spiral membrane elements, indicating that the MFS is suitable to study and monitor biofouling.