Water with a low pH (less than pH 7) is acidic and will corrode copper pipes and brass fittings. This includes water heating cylinders. Installing a pH corrector will resolve the problem.
This type of problem normally occurs on borehole supplies and is a clear indicator that the water contains high levels of iron or manganese. The water entering the house may look perfectly clear, however, once air is introduced into the water e.g. through agitation in a washing machine or dishwasher, the iron precipitates and leaves …