Greywater is becoming increasingly popular as off grid homesteaders find ecological and cost effective ways to manage their wastewater.  In the dry tropics this is especially important as every drop of water in a dry environment becomes much more valuable.

During my time living in Hawai’i, I have heard many differing accounts of whether or not greywater is actually considered legal to use in Hawai’i.  So I went digging.

The short answer is that Greywater is legal in Hawai’i, but only in areas not serviced by the public wastewater system.  In addition, the disposal of greywater must meet certain guidelines to be considered safe.  Therefore, in most cases, plans will be needed to be approved in order to be considered legal.

So what is greywater and how do we design a system that will be allowed by the law?  Let’s dive in a little deeper to learn more.

Before we begin, I’d like to mention that I professionally installed greywater systems in CA for 3 years.  I may break away from what the Hawaii Department of Health recommends because some of their guidelines are outdated and have not been revised.

Related: If you decide to install your own greywater system based on the directions below, you’re going to need a good pair of pipe cutters to get the job done easily.


What The Law Says About Using Greywater In Hawai’i

According to the Hawaii Department of Health, which has been tasked for creating guidelines for residential greywater use:

The Hawaii Legislature has urged the Department of Health to develop gray water recycling guidelines in House Resolution 290 of the twenty-fourth Legislature in 2008 and House Concurrent Resolutions 266 of the twenty-fifth Legislature in 2009.

In response, the Department of Health has developed these guidelines, which are intended to provide homeowners of single family dwellings with enough information to decide if a gray water system is right for them.

As of April 2009, all four counties in the state are waiving the portions of the Uniform Plumbing Code (UPC) to allow the use of washing machine wastewater to be used for subsurface irrigation. These waivers apply only to areas not serviced by a publicly owned sewer system.

The Department of Health will be the regulatory agency responsible for the gray water systems located in areas not serviced by publicly owned sewer systems. The Counties will retain regulatory responsibility for the areas serviced by their sewer systems. 

So what does this mean?  If you have a home in Hawai’i unable to connect to the public wastewater system, you can install a laundry to landscape greywater system without the need for approval.  

Any other greywater source (ie sinks, showers, etc) would need prior approval by the Department of Health.  If you are in an area serviced by a sewer system, you will need to seek County approval.

Related: Is It Legal To Go Off Grid In Hawai’i?

What Is Greywater?

Residential Wastewater is divided into 2 types:  Blackwater and greywater.  Blackwater is considered water from toilets and any sinks used for food preparation.  This type of water should never be reused for irrigation because it has a high risk of contamination by viruses and pathogens that can cause disease.

Greywater covers the rest of the water that you use in your home.  This will include water from:

  • Showers & Tubs
  • Laundry Machines (excluding poopy diapers and such)
  • Bathroom sinks
  • Any other wastewater that does not come in contact with toilet or food waste

Greywater is also a resource.  When you use greywater to irrigate your landscape, you are reducing your water usage, reducing the load that enters the wastewater treatment system and reducing the harm that concentrated amounts of wastewater causes to the environment.

It is estimated that 50%-80% of household water usage is greywater and the average household use for an american family is 300 gallons per day!  That is a lot of water.  If you are living in a dry environment, this is definitely a resource that you need to use in your garden. 

Even in wet climates, greywater is a welcome addition to the landscape because of the nature of some of the soaps and detergents that are used.  By choosing a greywater safe soap or detergent like Oasis or Ecos, the chemicals in those products actually break down into fertilizers to feed your plants!

Related: Off Grid Water Harvesting

Greywater Health and Safety Issues

There are health risks and safety issues associated with greywater if not managed in the proper way.  When I was younger, I apprenticed on a farm that had tried to install a greywater system by having it placed into a storage tank before going out to the landscape. 

That storage tank got nasty.  Some folks got Staph which may or may not have been related.  I am sure that the unhygienic nature of the system was a contributing factor to the overall decline in health in some of us who stayed there.  Once we got rid of that storage tank, things began to turn around.

  • Greywater should never be sprayed, only subsurface irrigation is allowed. 
  • If a storage tank is to be used, the water should be stored for no longer than 24hrs.  I would NOT suggest storing greywater in tanks although the Department of Health recommends an over engineered system that includes storage tanks for greywater that does not come from the laundry.
  • The location of the outflow of greywater shall be no closer than 15 ft to the property line. 
  • Do not use greywater on fruits and vegetables that may come in contact with the greywater, ie lettuce, root crops…NO.  Zucchini and fruit trees…YES.
  • Do not use greywater to wash down surfaces
  • If anyone gets sick with an infectious disease, reroute the greywater back to the wastewater treatment system, if you have one.

Tropical Plants That Like Greywater

When it comes to sending out greywater into the landscape, where do you send it to?  Not every plant is going to welcome the addition of a new water source.  But there are some who thrive on greywater.  

The chart below lists a few of the tropical plants that will welcome the addition of greywater.  If you have the opportunity to send your greywater out to one of these plants, they will do a great job absorbing that water and breaking it down before it has the chance of causing any issues.

My favorite plant to send greywater to is banana.  It just loves to eat.  If you use quality detergent that breaks down into fertilizer, your bananas will thrive!

BananaGingerAkiaBermuda grass
CoconutHeliconiaAkulikuliSeashore Paspalum
SugarcaneOrnamental TaroBeach Naupaka
PapayaTi LeafPohinahina

How To Install a Laundry To Landscape Greywater System

The best way for anyone to install a legal greywater system in their home is by installing a Laundry to Landscape Greywater System, developed by Art Ludwig at Oasis Designs and refined by Greywater Action.  The process is easy and in the majority of cases it does not require you to cut into any existing plumbing to make it work.

The magic of the system lays in the 3 way valve (Amazon Affliate Link) shown in the image below.  Depending on the position of the valve, you can either send it back into the wastewater system where it was going all along, or divert it to a newly plumb 1” pipe equipped with air vent that leads the laundry water out into the landscape.

When I install these systems, I use 100% PVC when inside the home.  As soon as that PVC exits the building, I switch to 1” Polyethylene tubing, the same stuff drip tubing is made of. 

If this is not available you can continue using 1” PVC, but it is not as easy to maneuver when placing it into the landscape.

I will lead the greywater thru the 1” pipe to mulch basins that are at least 3’x3’x1’ deep.  These basins are essentially holes dug into the ground that are then filled with mulch.  Place these mulch basins near plants that you would like to get watered.

I estimate one mulch basin per 10 gallons of water, just to make it simple.  So if I have a laundry machine that uses up 30 gallons of water and I do 2 loads on the same day, I will send that water out to 6 different basins.  If I only do 2 loads a week, but space each one out to different days, I will stick with 3 mulch basins.

As the 1” greywater line comes close to the basin, I will insert a 1” tee that reduces to ½”.  That ½” drip tubing goes to the basin through a hole drilled into the top side of a valve box (Amazon Affiliate Link).  Inside the valve box I will install a ½” on/off valve onto the ½” tube that entered the pre drilled hole on the side of the valve box. 

Bury the valve box in the much so that the top is at ground level and ensure that the greywater inlet has at least a 2” – 3” drop before the water hits the mulch inside of the valve box.  Do not have the greywater inlet buried in the mulch, nor do you want it discharging above the surface.  See image below.

That’s pretty much it.  Of course, you’ll want gravity on your side when disposing the laundry water into the landscape, but it can manage a slight elevation change due to the pump in the washing machine.

And remember, do not store the water.  Send it straight out into the landscape.

Related: Are Compost Toilets Legal In Hawai’i?

Branched Drain Greywater System For Hawai’i

What about the rest of the water in the house?  The shower water? The bathroom sinks?  How can I divert that water into the landscape?  Great question.  

The only problem is, it is not as easy as the laundry to landscape system.  The Hawai’i Department of Health recommends a highly engineered system that utilizes a holding tank.  These systems are best for commercial projects that need to accommodate very large flows.

When I was installing greywater systems in California, I learned a much easier way to send water from the shower and bathroom sinks to the garden.  The problem is, I don’t think the state of Hawai’i would consider it legal from what I could find out.  But I’m going to try and explain how to do it anyhow.


This system has been dubbed, the Showers to Flowers Greywater system, developed by Art Ludwig at Oasis Designs.  It works on the same concept as the laundry to landscape system in which it utilizes a 3 way valve to control where the water goes. 

First, you must have access to your plumbing, a house on a slab may not qualify for this project.

Find the 1.5” or 2” drainpipes coming out of your shower and bathroom sink.  I like to look for where those 2 pipes meet to install my automatic 3-way valve (Amazon Affiliate Link).  Cut the pipe and glue on the three-way valve to the pipe.  Install the actuator and run the wire up into the bathroom where you want the control switch to be located.

From where you installed the three-way valve, you now have an extra port that will allow the water to flow out into the landscape.  The opening will either be 1.5” or 2” depending on your plumbing.  We are going to connect ABS pipe to the open port on the 3-way valve and send it out from under the building to where you want to use the greywater.  Gravity needs to be on your side.

Once out from under the house you will need to pre dig the ditches and mulch basins where the greywater is to end up.  Everything must have at least a slight downward slope.  The magical part that makes the water distribution happen is called the Double Ell.

The Double Ell is essentially a “T” for ABS pipe that splits the flow evenly.  So when the greywater hits the first double ell it gets split 50/50.  At the next double ell, the water will be split 50/50 again, but only be a ¼ of the flow before the first double ell and so on.

There must be at least 2’ of straight run before installing the double ell.  When your piping finally makes into the mulch basin, you will want to install it into a valve box that has a hole drilled on the side for the abs pipe to fit (similar to the laundry to landscape system). 

Fit an on/off valve on the end to control the flow and make sure the valve box top is at ground level.

That’s it.  It is pretty much just like laundry to landscape system, but the piping needs more precision when being installed.  It is a great way to reuse that water though.  Way better than those over-engineered systems.


Why Do I Use Greywater?

Water is such a valuable resource.  It makes total sense to treat it as well as possible.  The idea of reusing one’s water instead of dumping it just makes plain sense.  

When I was building my home, How I dealt with my wastewater was not too well thought out.  I just sent pipes out from under my house to somewhere in the yard.  But I could see that I was wasting a resource.

Eventually I installed mulch basins where I can send my water too.  It makes me happy to see my plants getting watered from water that gets multiple uses before it leaves my site.  The off grid spirit is to be resourceful and reuse what you have.  Greywater is a perfect example of it.


Greywater Action
Art Ludwig
Hawaii Department of Health

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