A device (1; 201; 301) for capturing a first portion of a liquid flow, the device comprising: - an inlet (2; 202; 302) for receiving the liquid flow; - an outlet (4; 204; 304); - a guide (3; 203; 303) connected between the inlet (2; 202; 302) and the outlet (4; 204; 304), and adapted for directing a subsequent portion of the liquid flow to the outlet (4; 204; 304); the guide (3; 203; 303) comprising a displaceable element (6, 206, 210; 306); and - lifting means (69; 169; 369) for displacing the displaceable element from a first to a second position wherein - the outlet (4; 204; 304) is adapted for draining an excess of the liquid flow; - the guide (3; 203; 303) is adapted for directing the first portion of the liquid flow towards a reservoir (5; 205; 305) connected to the guide (3; 203; 303); - the displaceable element (6; 206; 210; 306) has a predefined shape with a first channel (63; 363) extending from a first opening (64; 364) to a second opening (65; 365), such that, when the displaceable element (6; 206; 210; 306) is in the first position, the first opening (64; 364) is in fluid connection with the inlet (2; 302) for receiving the first portion of the liquid flow so as to direct the first portion through the first channel (63; 363) towards the reservoir (5; 305), while blocking passage of liquid between the inlet (2; 202; 302) and the outlet (4; 204; 304), and wherein the predefined shape is adapted for blocking passage of liquid between the inlet (2; 202; 302) and the reservoir (5; 205; 305) while creating passage of liquid between the inlet (2; 202; 302) and the outlet (4; 204; 304) when the displaceable element (6; 206; 210; 306) is in the second position; - the lifting means (69; 169; 369) is adapted for displacing the displaceable element (6, 206, 210; 306) from the first to the second position when the first portion of the liquid flow is captured in the reservoir (5; 205; 305). - an inlet (2; 202; 302) for receiving the liquid flow; - an outlet (4; 204; 304); - a guide (3; 203; 303) connected between the inlet (2; 202; 302) and the outlet (4; 204; 304), and adapted for directing a subsequent portion of the liquid flow to the outlet (4; 204; 304); the guide (3; 203; 303) comprising a displaceable element (6, 206, 210; 306); and - lifting means (69; 169; 369) for displacing the displaceable element from a first to a second position wherein - the outlet (4; 204; 304) is adapted for draining an excess of the liquid flow; - the guide (3; 203; 303) is adapted for directing the first portion of the liquid flow towards a reservoir (5; 205; 305) connected to the guide (3; 203; 303); - the displaceable element (6; 206; 210; 306) has a predefined shape with a first channel (63; 363) extending from a first opening (64; 364) to a second opening (65; 365), such that, when the displaceable element (6; 206; 210; 306) is in the first position, the first opening (64; 364) is in fluid connection with the inlet (2; 302) for receiving the first portion of the liquid flow so as to direct the first portion through the first channel (63; 363) towards the reservoir (5; 305), while blocking passage of liquid between the inlet (2; 202; 302) and the outlet (4; 204; 304), and wherein the predefined shape is adapted for blocking passage of liquid between the inlet (2; 202; 302) and the reservoir (5; 205; 305) while creating passage of liquid between the inlet (2; 202; 302) and the outlet (4; 204; 304) when the displaceable element (6; 206; 210; 306) is in the second position; - the lifting means (69; 169; 369) is adapted for displacing the displaceable element (6, 206, 210; 306) from the first to the second position when the first portion of the liquid flow is captured in the reservoir (5; 205; 305).