Water fastness determination studies are carried out in order to determine the resistance of dyed or printed textile products that will remain in the water for a short or long time to the effect of water. In other words, the resistance of these products to being kept in a certain amount of water at normal ambient temperature is measured. In these tests, contamination of dyes on adjacent undyed product is determined. The dyestuff molecules move from the regions where the concentration is high on the fiber to the regions where the dye is low. It is determined whether the color of the sample to be tested has a color change in pure water according to the standards and gives color to the accompanying fabric used.

Accompanying fabrics are made of different materials to determine the attitude of the colored fabric sample to be measured against other materials where it may be in the same environment. These are the fabrics in the densities and weights described in the standards. During testing, the accompanying fabric is sewn on the fabric to be tested.

A sample should be taken for single color fabrics and for multi-colored fabrics each sample should be taken separately. Each sample is placed between two escort fabrics and sewed together along one edge. Accompanying fabrics are two unpainted fabrics. One must be of the same fiber type as the fabric sample to be tested and the other must be of the type shown in the standard. For cotton, for example, the accompanying fabric should be wool.

After the applied process, the change in the color of the sample fabric and the pollution caused by the dyeing in the accompanying fabrics are determined by gray scale (TS 423-3 EN 20105-A03).

Water fastness in textile products to determine the color changes that may occur as a result of the fabrics remain wet and in this case contaminate other products is determined in accordance with the following standard:

• TS EN ISO 105-E01 Textiles - Color fastness tests - Part E01: Color fastness to water