Anyone who has watched a utility locator work has seen the colours: red lines across a lawn, blue flags along a kerb, a green stripe heading for the street. They follow a uniform colour code published by the American Public Works Association and adopted across the United States and Canada, so that an excavator in any city reads the same marks the same way. A sewer inspector who marks a camera locate in the wrong colour, or who misreads a mark already on the ground, creates exactly the confusion the code exists to prevent. This guide gives the code, the marking conventions and how to use them for a sewer locate.
Quick answer: green marks sewer and drain lines; blue marks potable water; red marks electric power lines, cables and conduit; yellow marks gas, oil, steam and other flammable or hazardous materials; orange marks communications, telephone, cable television and fibre; purple marks reclaimed water and irrigation; pink marks temporary survey marks; white marks the limits of a proposed excavation. A sewer camera locate is painted in green with the depth and the pipe size written beside it, and a proposed dig is outlined in white before 811 is called.
The colours
Red: electric power lines, cables, conduit and lighting cables. Yellow: gas, oil, steam, petroleum and gaseous materials. Orange: communications, alarm and signal lines, cables and conduit. Blue: potable water. Purple: reclaimed water, irrigation and slurry lines. Green: sewers and drain lines. Pink: temporary survey markings. White: proposed excavation limits or route. The colours are standardised in paint and in flags, and the same colour is used for both.
Why green for sewer
The code assigns colours so that the most dangerous utilities are the most visible: red and yellow for electric and gas, the two that kill. Green for sewer and drain is the same green used for sewer tracer wire, which keeps the trades consistent. A sewer inspector marks only in green and does not mark anything else, because a green mark is read by every excavator as a drain. Tracer wire follows the same convention.
What a mark means
A line or a row of flags marks the approximate horizontal centreline of the facility. The code allows a tolerance zone either side, commonly eighteen inches to two feet depending on the state, within which the excavator must dig by hand. Letters beside a mark identify the owner or the type; numbers give pipe size or number of ducts; a depth is sometimes written but is advisory. An arrow shows the direction the line continues; a bracket or a line across shows where it ends or turns.
Marking a sewer camera locate
With the sonde located, paint a green cross or a short green line on the centreline at the finding, with the estimated depth written beside it and the distance from the cleanout, and with the pipe size if known. Where the route has been traced, a green line or a row of green flags along it. Where the finding is a point to be excavated, outline the proposed dig in white as well, so the 811 locate knows where to look. Do not use any other colour for the sewer, and do not paint over another utility’s mark. Marking a dig covers the locate itself.
White before 811
The 811 service asks the person requesting a locate to mark the proposed excavation in white, so the utility locators know the area to cover. A sewer repair site is outlined in white paint or white flags before the call, and the sewer’s own green mark sits inside it. Calling 811 covers the process.
Reading marks already on the ground
A red line through the dig area is an electric cable and the dig stops until it is hand-exposed. Yellow is gas and the same. Orange is communications, damage to which is expensive rather than deadly. Blue is water. Green marks that are not yours are the public sewer or another contractor’s drain locate. Faded marks are still marks. Marks with offsets, a line painted a stated distance to one side of the facility because the centreline could not be painted, carry an arrow and a distance; read them.
Flags, paint and chalk
Paint on grass lasts weeks and on asphalt days; flags last until mown or pulled; chalk lasts until rain. Use paint and flags for a locate that an excavator will act on in the coming weeks, and chalk for provisional marks during the locate. On concrete and pavers use chalk or tape, since paint is permanent. Marking on asphalt and pavers and marking on concrete cover each surface.
Customers and marks
Homeowners sometimes resent paint on a lawn. Explain what each colour means and that the marks fade; offer flags where paint is refused. Photograph every mark with a tape to a fixed reference before leaving, so the position survives the paint.
Colours elsewhere
The APWA code is North American. Other countries use different schemes; the United Kingdom, for instance, uses a different set of colours for gas and electricity. A contractor working abroad learns the local code before painting anything.
Who uses which colour
Excavation contractors mark white and read everything. Utility locators mark their own utility’s colour. Sewer inspectors mark green. Landscapers and pool builders, who dig more than anyone, should know the code and often do not. Cameras for landscaping contractors, for excavation contractors and for pool plumbing cover the trades that need both the camera and the code.
Common questions
What colour is used to mark sewer lines?
Green, for sewers and drain lines, in paint and in flags.
What do white marks on the ground mean before digging?
The limits of a proposed excavation, painted by whoever is going to dig so the 811 locators know where to mark.
What does a red line on my lawn mean?
An electric power line or cable. Do not dig within the tolerance zone without exposing it by hand.
Related guides
See locating a camera underground, locators for deep pipes, and cameras for basement drains.