Provided is a water purifier comprising: a filter unit filtering water supplied from a water source, including a reverse osmosis filter; a discharge unit discharging water filtered by the filter unit externally; a flushing portion connected to the reverse osmosis filter; and a controller configured to flow water filtered by the reverse osmosis filter to the flushing portion, and to flush the reverse osmosis filter.

According to one embodiment of the present invention, a control method for a water purifier comprises the steps of: filtering inflowing water so as to generate purified water; extracting the generated purified water; measuring the flow rate of the purified water extracted per unit time; flushing a filter part by using purified water generated in the filter part, when the extraction of the purified water is complete; and draining the flushed water to the outside through a residential water outlet of the filter part, wherein, in the purified water generation step, discharging of residential water generated in the purified water generation step is blocked according to the accumulated flow rate during a one-time extraction of the purified water, calculated on the basis of the flow rate of the purified water.

A single-stage water treatment system may include a fine filtration module configured for receiving process material with a high suspended and/or dissolved solids content and for producing a concentrate and a permeate. The fine filtration module may include an elongate housing member, a plurality of tubular membranes arranged within the elongate housing member and comprising elongate tubular members having membranous sidewalls with a selected permeability, a pair of end caps configured for controlling the flow of the process material within the plurality of tubular membranes, and an adjustment mechanism configured to adjust the elongation of the plurality of tubular membranes thereby adjusting the permeability thereof.

A single-stage water treatment system may include a fine filtration module configured for receiving process material with a high suspended and/or dissolved solids content and for producing a concentrate and a permeate. The fine filtration module may include an elongate housing member, a plurality of tubular membranes arranged within the elongate housing member and comprising elongate tubular members having membranous sidewalls with a selected permeability, a pair of end caps configured for controlling the flow of the process material within the plurality of tubular membranes, and an adjustment mechanism configured to adjust the elongation of the plurality of tubular membranes thereby adjusting the permeability thereof.