A method for removing sulphate, calcium and other soluble metals from sulphate-containing waste water, which method comprises the following steps a) a gypsum precipitation step, wherein the waste water is contacted with a first calcium compound or a first material comprising calcium compound to produce a first sludge containing gypsum, b) an ettringite precipitation step, wherein the first sludge is contacted with a second calcium compound or a second material comprising a second calcium compound and an aluminium compound or a material containing an aluminium compound, to produce a second sludge containing ettringite and gypsum, wherein a gypsum removal step is performed between steps a) and b) if the amount of gypsum solids precipitated in the gypsum precipitation step a) is more than 10 weight-% of the designed stoichiometric amount of ettringite solids precipitated in the ettringite precipitation step b), or wherein no gypsum removal step is performed if the amount of gypsum solids precipitated in the gypsum precipitation step a) is less than or equal to 10 weight-% of the designed stoichiometric amount of ettringite solids precipitated in the ettringite precipitation step b), c) a first separation step, wherein a solid-liquid separation is performed for the second sludge containing ettringite and gypsum to separate solids from the liquid thereby producing a first solution, d) a neutralisation step, wherein the first solution is contacted with a carbonating agent to neutralise the first solution and precipitate calcium contained in the first solution as calcium carbonate, and e) a second separation step wherein a solid-liquid separation is performed to separate precipitated calcium carbonate from the first solution in order to obtain water having a reduced sulphate, calcium and/or other soluble metals content. a) a gypsum precipitation step, wherein the waste water is contacted with a first calcium compound or a first material comprising calcium compound to produce a first sludge containing gypsum, b) an ettringite precipitation step, wherein the first sludge is contacted with a second calcium compound or a second material comprising a second calcium compound and an aluminium compound or a material containing an aluminium compound, to produce a second sludge containing ettringite and gypsum, wherein a gypsum removal step is performed between steps a) and b) if the amount of gypsum solids precipitated in the gypsum precipitation step a) is more than 10 weight-% of the designed stoichiometric amount of ettringite solids precipitated in the ettringite precipitation step b), or wherein no gypsum removal step is performed if the amount of gypsum solids precipitated in the gypsum precipitation step a) is less than or equal to 10 weight-% of the designed stoichiometric amount of ettringite solids precipitated in the ettringite precipitation step b), c) a first separation step, wherein a solid-liquid separation is performed for the second sludge containing ettringite and gypsum to separate solids from the liquid thereby producing a first solution, d) a neutralisation step, wherein the first solution is contacted with a carbonating agent to neutralise the first solution and precipitate calcium contained in the first solution as calcium carbonate, and e) a second separation step wherein a solid-liquid separation is performed to separate precipitated calcium carbonate from the first solution in order to obtain water having a reduced sulphate, calcium and/or other soluble metals content.