Always work using clean materials (sponges, brushes, spatulas, water bowls) and change the water regularly.
General tip: Water Make-up can be used to add (additional) colour to the hair and eyebrows, provided that the hair is not permed, bleached or dyed. Use a toothbrush to do this. Hair that has been coloured using Water Make-up (Pure) can be washed with shampoo.