Purple pipes. Creative Commons photo by John Loo

~Purple drain, purple drain…I only wanted to see you bathing in the purple drain~. Creative Commons photo by John Loo

Across many recently installed California commercial landscapes, purple pipes snake through planting beds.  Did you ever wonder about their purpose and if they really do keep plants hydrated?  As an urban horticulturalist, I wondered exactly the same thing. Also, why did they choose that particularly unusual color of purple?

Coming from the land of eternal rainfall, Louisiana, there was never a need for an underground landscaping irrigation system. Now here in Los Angeles, in a Mediterranean/near-desert climate, I’ve noticed purple pipes everywhere.

The History

The Irvine Ranch Water District has a fascinating history about the purple pipe program on their website. In the early 1960’s, this district began producing recycled water.  Once wastewater reaches their water treatment plants in Irvine and Los Alisos, California, it takes anywhere from 16 to 18 hours to generate 28 million gallons of non-potable, recycled water.  That’s incredibly fast and an amazing fact!

In the 1980’s when lavender Ralph Lauren polo shirts were all the rage, a head engineer at the IRWD asked another engineer – who happened to be color blind – which color of pipe best stood against the color white.   It wasn’t fashion that drove his decision, but a hue of gray that stood out from the rest according to IRWD Principal Engineer Steve Malloy.  If it looked different to his color blind eyes, others on the job site would recognize those pipes too, even if they were color blind.  The IRWD worked with the American Water Works Association to make “Irvine Purple” the international standard color symbolizing recycled water.

Where do all these purple pipes go? A great deal of irrigation water is necessary to keep California landscape green. You can find these purple pipes at sites such as freeways, industrial processes, flushing toilets in some office buildings, and even in cooling towers.

Photo: CC0 1.0 Universal (CC0 1.0) / Public Domain Dedication

Photo: CC0 1.0 Universal (CC0 1.0) / Public Domain Dedication

Can you just tap into these purple pipes to help reduce your impact on our supply of available drinking water?  The answer is unfortunately, ‘no’.  But maybe not for long if Solana Beach’s Dave Ferguson has the final word. He lives just 6 inches from an exposed purple pipe that irrigates the iceplants surrounding his home. City and county officials say it cannot be done for a sundry of different and unclear reasons. Yet, in the City of Irvine a Free Recycled Water station is ready to meet Irvine citizen’s irrigation needs. Bring your jug, your identification, and you are ready to lug that stuff to a thirsty water saving plant. Not quite the straw to your landscape, but definitely one step closer. Pretty cool, huh?  According to the IRWD website, “hundreds of residents have benefitted from the resource.”

Recycled Water vs. Gray Water 

The purple pipe keeps recycled water separate from other types of water delivery systems, such as drinking water and waste water infrastructures.  Besides cities and home owner associations, some large tree and shrub nurseries recapture, treat, and reuse their recycled water on their crops and landscape plantings.  So, is recycled water the same as gray water?

Water from the purple pipe is different than gray water.  Both are not potable, but recycled water is cleaner and safer than gray water, which comes with more restrictions on its usage according to cities using recycled water.  The City of Palo Alto determined that recycled water is much saltier than drinkable water. When residents started irrigation with water from purple pipes, it clearly damaged the sensitive roots of Azaleas, Buxus, Taxus, Liquidamber, Citrus, Camellias, and Rhododendron. Do you see a pattern here?

All of the affected are acid loving plants, and salt-laden water tends to be alkaline. So the obvious question you might ask is, “Can you use seacoast appropriate plants and apply water that comes from the purple pipes onto any of them?” The answer is ‘yes’…but only if their roots like it.  Not all plants that enjoy salty environments are tolerant of highly alkaline water.  Here are a few that are:  Pittosporum tobira, Plumbago auriculata, Euonymus japonica, Rosmarinus, and Dietes.


Lessons Learned

AHBE Landscape Architects chipped in at a volunteer service day known as Green Apple Day at Playa Vista Elementary in late September.  Lots of clean up needed to be completed prior to the national meeting of US Green Building Council Greenbuild and a tour filled with a bus load of sustainability experts, which was scheduled that following week.  We needed to conduct site check with the principal and an architect from NAC. It gave us a perfect opportunity to explore and research a landscape project designed by AHBE Landscape Architects over 5 years ago.  I saw how plants were affected by the salty water from the purple pipes.

We carefully took soil samples from around the areas where plants were clearly underperforming to confirm salt damage. We patiently waited for the results, and one of the project managers even volunteered to hunt inside boxes of stored documentation to find the original soil samples. The areas tested also had a faulty irrigation system, but where it was somewhat working the soil report showed very high salinity. Since it is close to the beach, the salt water table is higher. But these statistics were off the chart. That said, the purple pipe contributes to a higher than normal alkalinity


It’s already a challenge to limit water usage as a Los Angeles resident. Now we’re aware that the water delivered through these purple pipes must be carefully considered too, making creativity even more challenging (though much more rewarding when a solution/application is reached). Recycled water is available to irrigate our residential landscapes, yet we’re unable to tap into that delivery system to keep our landscapes healthy and productive is disturbing.

I am very happy to have recycled water to rely on at most California commercial sites, but the water delivery infrastructure and enhanced water quality definitely should be taking precedent to help ease the drought. Until then, I will just enjoy my glass of water from the tap, and continue paying a premium to use it on my residential landscape.

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  1. Jodie Cook #
    December 24, 2016

    Great history of purple pipe, Kathryn. I had no idea it originated in Irvine. Soil salinity is at its most concentrated in late summer and early fall before our cleansing rains. As we continue to move away from high-water exotics and toward the best of our CA and southwest native, climate-adapted plants we won’t be so affected by summer soil salt buildup in recycled water.

    Once we get serious about contouring land for rain not runoff, building living soil, reducing soil-compacting maintenance regimes and using plants that evolved in our summer-dry climate it won’t be such an uphill slog trying to keep the wrong plants healthy in lifeless, compacted soil with irrigation water that makes them sick. Rather than hoping recycled water will save our thirsty landscapes, it might prove to be our wake up call to do things differently.


  2. Katharine Rudnyk #
    January 3, 2017

    Hi! Jodie, Happy New Year! May it be the one where purple pipes become a norm within our residential areas as well as its current application on certain commercial and civic plazas. You are correct, noting that the soil’s alkalinity drastically changed from the originally measured pH at the project’s inception taken around the same time of the year. We have seen the same type of results from other projects utilizing purple pipes. Perhaps we can go out after the rains and the system has been repaired to see if we get similar or hopefully, better results for this particular project. Glad to have this type of water as available resource, definitely better than none! KAR


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