The City of Hopkins filters iron out of the water before it reaches your home. After the water is filtered the remaining iron content is 0.03 parts per million. Even though the City filters out the iron, some iron still remains in the water and coats the inside of the water main pipes. Your water turns brown because of the release of these mineral deposits, caused when large amounts of water are pulled off the system either by hydrant flushing, water main breaks, water service leaks, or the Fire Department.