10 The development of 3D printing in recent years opens up a vast array of possibilities in the field 11 of flow analysis. In the present study, a new 3D-printed flow system has been developed for 12 the selective spectrophotometric determination of lead in natural waters. This system was 13 composed of three 3D-printed units (sample treatment, mixing coil and detection) that might 14 have been assembled without any tubing to form a complete flow system. Lead was determined 15 in a two-step procedure. A preconcentration of lead was first carried out on TrisKem Pb Resin 16 located in a 3D-printed column reservoir closed by a tapped screw. This resin showed a high 17 extraction selectivity for lead over many tested potential interfering metals. In a second step, 18 lead was eluted by ammonium oxalate in presence of 4-(2-pyridylazo)-resorcinol (PAR), and 19 spectrophotometrically detected at 520 nm. The optimized flow system has exhibited a linear 20 response from 3 to 120 µg.L-1. Detection limit, coefficient of variation and sampling rate were 21 evaluated at 2.7 µg.L-1 , 5.4% (n=6) and 4 sample.h-1 , respectively. This flow system stands out 22 by its fully 3D design, portability and simplicity for low cost analysis of lead in natural waters. 23 24