Rusty plumbing pipes can be a major problem. Eventually the rust will eat through the pipes and major leaks can occur.
What types of pipes are rust-prone?
Galvanized and cast iron pipes are the two types that are most likely to rust. The main difference is in where they rust. Galvanized pipes form rust first on the inside of the pipe, and rust may never make its way to the visible outside before problems begin to surface. Rust is most likely to occur around the joints where two pipes thread together. Cast iron pipes may rust from both the inside and the outside. Generally, rust first begins on the weakest part of the pipe, which means at a seam or joint, or somewhere on the top surface.
Why does the rust form?
The most common cause of rust on your water pipes is some sort of damage that opens the metal up to oxygen exposure and thus rust. It could be a simple scratch or abrasion, such as from hard minerals in the water repeatedly rushing through the pipe. Damage also results from age as the metal may eventually begin to weaken and become more prone to rust formation. Past repairs that scuffed or dented a pipe can also lead to rust.
Does rust always mean there is a leak?
Rusting is at an advanced stage once a leak begins, but there are usually some early signs that the problem is developing. When rust forms inside the pipe, you may notice low water pressure and reduced water flow as the rust blocks up the pipe. The water may also have a red, orange, or brown hue. Rust on the outside is most easily spotted by visual inspection of any accessible plumbing lines. You can use a mirror to check the back surfaces of any pipes that you can't easily access from behind.
How can rust be repaired?
In many cases, rust can't be repaired. If the issue is caught early on the exterior of a cast iron pipe, it can sometimes be sanded off and the area sealed to prevent future oxidation. On galvanized pipes, it's usually not possible to repair since the rust is on the inside and not accessible. If you want to make sure rust is no longer a concern, the best solution is to have a plumbing contractor replace your outdated metal pipes with rust-proof PEX plumbing pipe.
Contact a residential plumber if you suspect that rusty pipes are a problem in your home.