System for purifying a liquid

A liquid purification system, comprising:

• a raw liquid feed valve configured to mount to a raw liquid feed line;
• a filtration unit comprising:
• a liquid purification unit with an inlet for raw liquid and an outlet for purified liquid and an outlet for drain liquid,
• a means for maintaining pressure,
• a raw liquid/concentrate supply line to supply a mix of raw liquid and concentrate formed in a liquid purification process to the liquid purification unit,
• a liquid mixing device comprising a pressure tank having a first cavity and a second cavity separated by a flexible partition and connected to the raw liquid/concentrate supply line to supply a mix of the raw liquid and the concentrate to the liquid purification unit from the first cavity, the liquid mixing device connected to receive the concentrate into the first cavity from the liquid purification unit in a way to build pressure within the liquid mixing device by compressing the second cavity during receiving the concentrate during the liquid purification process,
• a recirculation line,
• a purified liquid line,
• a drain liquid line connected to the outlet for drain liquid,
• a circulating liquid flow maintenance means disposed in the raw liquid/concentrate supply line upstream of the liquid purification unit, and
• a drain discharge valve disposed in the drain liquid line,
• wherein in response to opening the drain discharge valve, the drain discharge valve, the liquid mixing device, and the liquid purification device are connected such that drain liquid from the first cavity of the liquid mixing device drains through the liquid purification device using the pressure built in the liquid mixing device with the flexible partition during receiving the concentrate during the liquid purification process and at a drain liquid velocity exceeding a liquid velocity for liquid driven by the means for maintaining pressure, the drain liquid discharging while simultaneously reducing an amount of the concentrate in the liquid mixing device.