Dual piping (water)

Dual piping is a system of plumbing installations used to supply both potable and recycled water to a home or business. Under this system, two separate water distribution systems with completely separate piping are used to deliver water to the user. This system prevents mixing of the two water supplies, which is undesirable as recycled water is not intended for human consumption. Recycled water is used for landscape irrigation, industrial processes (typically as a coolant), and sometimes for flushing toilets.

In the United States, recycled water is distributed in purple colored pipes known as "purple pipe" to alert users that the pipes contain non-potable water.