If you turn on your faucet and light brown water comes out, there is most likely some presence of iron or manganese in your water system. Often times the galvanic coating comes off the inside of water pipes or the magnesium comes off of the anode rod, which exposes the iron and therefore gives the water a hint of brown coloring. It is important to determine whether the brown water comes from the entire water system or just part of it.
If you turn on the hot water and see brown, then the anode rod in the water heater needs to be replaced or the entire water heater itself may be malfunctioning (water heaters have a lifespan of roughly 10-15 years).
If you get brown water from both the hot and cold water systems, then the problem lies within the main water pipe before it branches off to different parts of the house. These plumbing problems are a bit more difficult to treat and may require help from a plumbing contractor.
You can read more about replacing an old water heater here if you would like to make it a DIY plumbing repair. For plumbing service calls, dial 1 800 GET ROTO or search the internet for your local Roto-Rooter number (i.e. "Plumber Salt Lake City" or "Plumber Philadelphia").