DIY: Simple Grey Water System / by keith messick


Water is the most precious commodity on earth. We cannot live without it. In fact, we can only live about three or four days without it. We should be preserving, protecting, reusing and recycling water whenever possible.

Most residential irrigation systems use the city’s/county’s municipal water supply. While it is often the only choice, it really does not make sense to use clean, drinkable water on the landscape.

Grey water is the waste water from all sources in a residence except the toilet. A gray water system captures water that is used for showering or washing clothes and makes it available to irrigate the landscape.

There are upfront costs to install a grey water system. But once hooked up and running, it requires very little maintenance.

This system irrigates trees and plants from the water collected from two showers. For consistent irrigation, it requires people to be showering on a regular basis. If the residents were to take a vacation for more than a week, the trees and plants may need a back up source of water.

Recycling water is good for the environment and will save you money as the cost for clean water is likely to increase every year.

Grey Water Systems

The level of complexity for grey water systems vary. They can range from very simple rain water collection to fully automated whole house filtered and pumped irrigation systems.

How and where grey water systems are installed and operated are now covered under the building code. To be legal, a grey water system should be permitted and inspected through your local planning and building department.

The system described here is not fully code compliant and was not fully inspected and permitted. However, it is simple, safe, and efficient.

Sources of Grey Water

Showers: Best

Bathroom/Laundry Sinks: Good

Washing Machine: Good

Kitchen sink/Dishwasher: Not good-too much solid food waste

Probably the most challenging issue is finding/accessing a source of grey water. A good source of grey water will be water that is fairly clean without a lot of solids. Sources of water with solids will clog the system.

The system described here is simple and low tech. It is only capturing the water from two showers and a washing machine. (The washing machine source on this system, while available, was not used) If we tried to capture all sources of waste water, except the toilet, this water would have to be filtered to remove solid material such as food waste. And this filter would have to be checked, cleaned, and replaced on a regular basis. This may be fine for some applications (and will probably be the way of the future, eventually), but the system here is simple to use and requires very little ongoing maintenance.

Washing machines can be a great source of grey water. However, with front loading washers being so efficient, there is very little water to capture. The typical top loading washers, however, are a good source of grey water..

System Design

A plan view of the system

The system shown here is easiest to install during new construction. But it could be fairly easily retrofitted to a house with a raised foundation.

The overall system design involves modifying plumbing from a shower drain, an exterior valve, 1.5” ABS pipe/fittings, a catch basin, and a pump.

This system irrigates several fruit trees and then the excess grey water is captured in a catch basin. A pump with a float switch then automatically pumps the excess water out of the catch basin to a large flower bed. This last step, with the pump, can be omitted based on the available slope you have on your site.

The total cost of this system was less than $200.

The start of the System-Ball Valve #1

System Components

Plumbing-Shower Drain

One special feature of this system is the way it is plumbed. The plumbing from the shower is configured such that water is automatically diverted to supply the grey water system. If and when the exterior valve is closed, grey water stops flowing to the system and simply drains back into the city sewer system (as though there was no grey water system). There is no complex valving to worry about. The system is either on or off.

A section drawing showing how water comes from the shower.


A valve is located on the exterior of the foundation stem wall, where the supply drain line emerges from the crawl space. This valve allows the system to be turned off. You may want to close the valve during winter time when less water is needed in the landscape.

Ball Valve #1-From shower

Ball Valve #2-From shower

Exterior Plumbing-ABS Pipe

Pipe from valve #1

Pipe at left is from valve #1 / Pipe at right is from valve #2

Both pipes headed to the catch basin

Passive Irrigating Pipe-1.5” ABS pipe with 1/4” holes drilled in it.

For the most part, the system is gravity fed. The water exits the house and runs down hill. 1.5” ABS pipe and fittings were used throughout to transport the water. The pipe sizes are relatively large to avoid any possible clogs (there will be some hair and soap moving through the pipe). The pipe and fittings are inexpensive and easy to get at any big box supply store.

Up until the pump, there is essentially no pressure in the pipe. The water is passively flowing down hill. The on/off main system ball valve was attached with a 2” flexible coupling. The 1.5” ABS pipe was pushed into the ball valve and held by friction. This could be glued in, but the fit is very tight and requires no glue to stay put. (if you choose to glue this connection, you will need an ABS/PVC cement).

The long runs of pipe were glued together with ABS cement. The ABS pipe will not stay together without glue (called ABS cement). The various fittings used are shown below.

A “valve” was made to control the flow of water at each fruit tree. This consists of a sanitary T, a very short piece of pipe, and a cap with a few holes drilled into it. The sanitary T is glued in to the main line, which is simply gravity fed. The cap and small piece of pipe is pushed into the sanitary T and held by friction. The cap does not need to be glued in. To control the amount of water that comes out of the hole in the cap, the cap is rotated to a position that delivers the right amount of water.

Depending on the amount and velocity of the flowing water in the pipe by each tree, each “valve” (the drilled cap) is rotated to deliver just the right amount of water. The flow of water by each tree is greatly effected by the slope of the pipe at that point. This is a low tech system. While the slope of the pipe is downward, it is not a perfect slope. At some points there is more slope than others. At these points, the water is flowing faster and the valve must be rotated to capture this flowing water (the water in the pipe will be more shallow than in a slow flowing, less sloped, pipe).

You may want to experiment with the right size of hole to drill in the cap. Start with a small hole. If this does not deliver enough water, you can increase the size of the hole. Remember that a small hole may get clogged.

“Valve”-Sanitary T, short pipe piece, and drilled cap

“Valve”-Drilled cap

“Valve”-Drilled cap and short length of pipe

There is a sanitary T at the ends of the pipe runs to allow for cleaning/flushing of the pipe. The ends are capped with a flexible cap (they leak otherwise). The pipe is also held in place by short lengths of rebar hammered into the ground next to the pipe. Pre-bent rebar was also purchased to hold the ABS pipe down. While the pre-bent rebar was advertised to be 2.5” wide, it had to be bent open a little more (it was not as wide as it claimed to be). The rebar helps keep everything stable in case the pipe gets kicked.

When the entire system is complete, everything will be covered by mulch.

Flex cap at the end of pipe allows for cleanout / flush

Rebar is used to hold pipe in place

Rebar hook around ABS pipe

Rebar hook

Catch Basin

The fruit tress don’t utilize all of the water that is available in the pipe. (A typical shower is 25-40 gallons of water). The remaining water is captured in a basin at the end of the run. The basin holds about 22 gallons of water.

Catch basin

Catch Basin-Finished-1. Top Pipe = ABS pipe for extension cord, 2. Middle Pipe = ABS Pipe for grey water in, 3. Bottom Pipe = ABS pipe for grey water out

ABS pipe that contains & protects the power cord / Power Connection


The level (amount) of water in the basin is controlled by a float switch attached to a pump. A float switch is a mercury switch inside a sealed float. The float switch will automatically turn the pump on and off depending on the level of water in the basin. The excess water is automatically pumped out to a large flower bed.

At the flower bed, a passive irrigating pipe was created. This is simply a piece of 1.5” ABS pipe (see picture above) with 1/4” holes, 3” apart, drilled in it. The pipe is somewhat flexible. It was gently curved with the line of the flower bed.

A check valve should be installed on the pump to keep the pump from siphoning the water back into the basin (without the check valve, the water is drawn back into the basin after the pump turns off). The power cords will be run through a 2” PVC pipe back to the wall outlet.

As mentioned above, the pump can be optional depending on the slope available at the site. In this application, the termination of the excess water, a large flower bed, was at a slightly higher elevation. A pump was necessary to get the water to that final destination.

Pump-Float switch can be seen attached to the power cord.

Pump sits at the bottom of the basin

Sustainable / Save Money

Finished Grey Water System-Covered in mulch

Water is the most precious commodity on earth. We should be doing everything we can to preserve and protect this vital resource. And reuse and recycle water whenever given the opportunity. Creating a grey water system is a simple step in the right direction to support this effort.