## 3 Results  
In the present study, monitoring the generation and accumulation of charge in the cell in the water supply system was performed at the following flow rates: 0.9, 1.8, 3.6, 5.4 and 7.2 mL/min. The corresponding \(\Delta q(t)\) dependencies are shown in Figure 2.  
As seen from Figure 2a-e, a linear-stepwise mode of charge accumulation (which we observed earlier at the 0.9 mL/min flow rate [30]) is observed over the entire range of flow rates studied. In Figure 2a (curve 1), for instance, from 0 to 2.5 min, a linear, slowly increasing section of the curve with a gradient (\(\Delta q/\Delta t\)) of \(\sim\)0.1 nC/min is observed. This is followed by a \(\sim\)2.5-nC jump with a 5 nC/min gradient for 0.5 min. Then, a further slow linear increase in charge accumulation with a gradient of (\(\Delta q/\Delta t\)) \(\sim\)0.2 nC/min is observed. For curve 2, a stepwise accumulation of charge is observed from the very start of the observation time. For curves 3 and 4 in Figure 2a, the appearance of jumps is observed from the second and third minutes, respectively. For all these curves, the amplitude of a jump was roughly of the order of 2 to 3 nC. For the four curves in Figure 2a, the total amount of charge (\(\Delta q\)) accumulated in the measuring cell for seven minutes was of the order of \(\Delta q\) =2.7 to 4.2 nC. Figure 1: Experimental setup. 1 is the reservoir with water; 2 is the silicone pipe (input section); 3 is the peristaltic pump; 4 is the silicone pipe (output section); 5 is the tip; 6 is the measuring cell with the connected electrometer; 7 is the electrometer; and Eg is the grounding electrode placed at a 15-cm distance from the tip nozzle orifice. A similar situation was observed for a water supply rate of 1.8 mL/min (see Figure 2b). The appearance of jumps is observed for all four curves. So, for curve 1, after the phase of slow accumulation of charge in the measuring cell with a gradient (\(\Delta q/\Delta t\)) of \(\sim\)0.7 nC/4 min, an appearance of a jump with a \(\Delta q\)\(\sim\)1.5 nC amplitude and (\(\Delta q/\Delta t\)) \(\sim\) 3 nC/min gradient for 0.5 min is observed at the 4 th min. For the four curves in Figure 2b, the total amount of charge accumulated in the measuring cell during the measurement time was of the order of \(\Delta q\) =2.2 to 3.2 nC. For the flow rate of 2.7 mL/min, both linear (curves 3 and 4) and linear-stepwise (curves 1 and 2) modes of charge accumulation in the measuring cell are observed. For the linear mode, charge accumulation with gradients (\(\Delta q/\Delta t\)) of 3.5 nC/7 min (curve 3) and 4.5 nC/7 min (curve 4) is characteristic, while for the linear-stepwise one, the appearance of jumps at the 1 st min (curve 1), or even at the very start of the measurement (curve 2), is typical. For the four curves in Figure 2c, the total amount of charge accumulated in the measuring cell for 7 min was from \(\Delta q\) =2.2 to 3.2 nC. It is to be noted that a drop-by-drop mode of water injection from the tip into the measuring cell was observed at flow rates from 0.9 to 2.7 mL/min. With further increase of the flow rate, in the range from 3.6 to 5.4 mL/min, a jet flow of water from the tip is observed. As seen from Figure 2d,e, despite the drop-by-drop mode of liquid flow from the tip changed to the jet flow, this did not lead to a disappearance of the stepwise accumulation of charge in the measuring cell. So, for a water flow rate of 3.6 mL/min, a linear-stepwise mode of charge accumulation (curves 1 and 4, Figure 2d) is observed alongside with a linear one (curves 2 and 3). For curve 1, the magnitude of the jump was of the order of 2 nC with a gradient of (\(\Delta q/\Delta t\))\(\sim\)2 nC/0.25 min for 0.25 min. At the same time, for curve 4 (Figure 2d), the appearance of two jumps with greater (3.6 nC/0.25 min)  
Figure 2: Typical time dependencies of charge accumulation (\(\Delta q\)) obtained upon the pumping of water with various flow rates: 0.9 mL/min (**a**), 1.8 mL/min (**b**), 2.7 mL/min (**c**), 3.6 mL/min (**d**), 5.4 mL/min and 7.2 mL/min (**e**).