Equipment for preparing and dosing liquid polyelectrolytes, which is compact and transportable, comprising a hydraulic injector wherein an initial premixing of water and flocculant is generated wherein said concentrated premixture of water and flocculant comes out of the injector and enters into a mixing tank, wherein said tank comprises an electric stirrer; the equipment also comprising an electromechanical dosing pump and an outlet hose of the liquid polyelectrolyte or diluted flocculant with an outlet valve and connected to the pump; wherein the equipment is characterised in that: the hydraulic injector comprises a cylinder and a set of internal valves of independent inlet of water and liquid polymer flocculant into de cylinder, being the injector fed by a solenoid valve for the inlet of water and a hose for the inlet of liquid flocculant communicating with a secondary tank of liquid flocculant; wherein the cylinder comprises an internal plunger which follows a vertical path inside the cylinder when the set of internal valves direct a flow of water inside the injector, and wherein said movement of the plunger regulates the suction of the flocculant from the hose, being the proportion of water and flocculant regulated by adjusting the length of the path of the plunger inside the cylinder and being the speed of the plunger proportional to the flow rate of water circulating through the injector; wherein the tank comprises at least one probe with a double level detection of the flocculant preparation for the maximum and minimum level, being the probe in connection with an electronic board for entering water into the injector; and wherein the electronic board comprises a control module for the operation of the equipment, being in connection with the probe, the hydraulic injector, the dosing pump, the solenoid valve, and the electric stirrer and comprising manual and automatic control means for the dosing and outlet of the liquid polyelectrolyte. the hydraulic injector comprises a cylinder and a set of internal valves of independent inlet of water and liquid polymer flocculant into de cylinder, being the injector fed by a solenoid valve for the inlet of water and a hose for the inlet of liquid flocculant communicating with a secondary tank of liquid flocculant; wherein the cylinder comprises an internal plunger which follows a vertical path inside the cylinder when the set of internal valves direct a flow of water inside the injector, and wherein said movement of the plunger regulates the suction of the flocculant from the hose, being the proportion of water and flocculant regulated by adjusting the length of the path of the plunger inside the cylinder and being the speed of the plunger proportional to the flow rate of water circulating through the injector; wherein the tank comprises at least one probe with a double level detection of the flocculant preparation for the maximum and minimum level, being the probe in connection with an electronic board for entering water into the injector; and wherein the electronic board comprises a control module for the operation of the equipment, being in connection with the probe, the hydraulic injector, the dosing pump, the solenoid valve, and the electric stirrer and comprising manual and automatic control means for the dosing and outlet of the liquid polyelectrolyte.