Water that leaves a public utility's treatment plant travels through pipes that may be rusted or cracked. When this happens, the clean water is contaminated with rust or whatever material it comes in contact with. In a study done by the New York Times, over 49 million people between 2004 and 2009 received contaminated water. If you have a wound in your mouth or your immune system is compromised, do not consume water that appears to be contaminated.
Rust is Safe
If the only thing wrong with water is that it contains rust, it is safe to drink. Rust can discolor water, but it does not harm someone who drinks it. In fact, the FDA has approved the use of rust (iron oxide) as a food additive. However, rust can stain clothes or plumbing fixtures, and can indicate a plumbing leak inside the building where it occurs.
Soil and dirt can include many different materials. Some of these are safe and some are not. Dirt can contain toxic metals, parasites and bacteria. All of these can be invisible to the naked eye. If you can see dirt in your water, it is best to boil it before drinking it or to drink bottled water.
If water is contaminated with dirt, it is wise to assume bacteria is growing in it. Any organic material in water can feed bacteria, and if your water is not chlorinated or is insufficiently chlorinated, bacteria grows when contamination is present. Not all bacteria is harmful when consumed, but some types can cause illness.
If there is a leak in a pipe, it is possible that the water has become exposed to sewage. Water pipes and municipal sewer pipes do run parallel to each other; often small sewer leaks are not repaired quickly because they do not cause the flooding water pipe leaks cause. If something such as frost heaving or tree roots damaged your water pipe, it is possible that a sewer line was damaged in the same way.
Many people associate rust with tetanus, and so are especially concerned about contracting this disease if exposed to rust. However, tetanus infects people through deep wounds, not through ingestion. Tetanus is a bacteria present in dirt as well as rust and people are exposed to it every day, especially in agricultural work, without becoming infected.