The present invention relates to a method of reducing the total organic carbon (TOC) content of waste water in the course of the preparation of concentrated solutions or suspensions of anionic organic compounds, which method comprises increasing the concentration of an aqueous solution or suspension of an anionic organic compound in the form of its free acid or its alkali metal salt, having a salt content of less than 5% of extraneous salt by weight based on the total solution or suspension, by microfiltration, ultrafiltration and/or nanofiltration, a) the membrane pore size being so selected that compounds having molecular weights in the range from 300 to 1000 Daltons or higher are retained, and b) the content of anionic compound in the concentrate being so adjusted to from 10 to 50% by weight that the total organic carbon (TOC) content of the permeate is less than 0.5% by weight, based on the total permeate, and c) optionally, after increasing the concentration of a suspension, dissolving the anionic organic compound by adding a suitable base. The invention relates also to the solutions and suspensions prepared by that means and to the use of such solutions or suspensions in dyeing or optically whitening paper or textile materials.