Because of a water main break along River Road, Highland Park residents have received a boil water advisory. The nature of the threat is that when water pipes lose pressure it becomes possible for contaminated water and dirt from the material surrounding the pipes to seep in. In a normally operating system the pressure from the water within the pipes serves to keep any foreign material from seeping in and introducing contamination into the water within the pipes.
A boil water advisory does not mean that the water is contaminated. It means that the water system operators cannot say for certain if any contamination exists. See the notice below from Middlesex Water on appropriate steps during a boil water advisory.