Water is delivered to your home or business through a network of underground pipes referred to as the distribution system. The principal pipe or conduit is called a main. Water mains in this distribution system can fail due to age, corrosion, high pressure surges, defective materials, or damage by construction work. Fire hydrants can also be broken off by vehicles. When a main breaks, the increased velocity of the water can pick up dirt and other materials that normally settle to the bottom of the pipes.

Every distribution system has mains that must be ended due to physical obstructions (rivers, roads, etc.) or city design features (sports complexes, cul-de-sacs,etc.). This results in a "dead end" that does not connect back with another main. Low usage in these areas results in sediment accumulation. Over time the lack of circulation can result in the appearance of discolored, foul tasting stale water.

The high velocity of water used to fight fires and to test fire hydrants can pick up sediment as described under main breaks.

Sometimes mains must be replaced or cleaned. Also, new buildings require connection to the existing water main. These and other similar activities may disturb the accumulated sediment and result in temporarily dirty water.

Dirty water often originates in the hot-water tank. Hot water tanks can accumulate sediment and therefore need to be flushed clean.

Defective plumbing can lead to many dirty water conditions. Pieces of rubber or plastic washers that age and crumble can result in particles in the water. Improperly joined dissimilar materials (such as iron and galvanized, or copper and iron) can accelerate corrosion and turn water red or green. Rapid shut-off of faucets or automatic valves in washing machines can cause tremendous pressure surges that dislodge material from pipe walls.

Improper attachments for insecticide sprayers or hoses attached to faucets can lead to back-siphonage and introduce unwanted materials into the house plumbing system. Contact Denver Water's Water Quality section for more information on identifying potential cross connections in your home.

First try flushing the toilet, and look into the bowl. Since the toilet uses only COLD water, if the bowl is clear, then the problem is with the hot water. If the bowl water is dirty, then the cold water is affected, and activities outside your home should be considered as the cause.
If the hot water is the source, the hot water tank must be flushed clean, according to the manufacturer's recommendations. If the cold water is the source, the cold water needs to be flushed. Don't continue to flush the toilet after the initial test. Don't use the hot water. Prevent further accumulations of sediment in the hot water tank by not using the hot water. If the dishwasher or clothes washer is running, stop it mid cycle until until the water is cleared up.

If distribution system repair or maintenance is underway, this may be the cause. Also look for street sweepers or anyone else using a fire hydrant.

Open the cold-water faucet in the bathtub all the way open, full force, with the drain open, for about 15 minutes. Most dirty water situations will clear up in this time. If not, turn the water off, wait 10-15 minutes, and repeat the flushing again.