[PDF]Making-Use-of-Grey-Water-in-the-Garden

Making Use of Greywater
in the Garden Tipsheet 5o P

Help save valuable clean water by reusing wastewater on your plants.

Machynlleth, Powys SY20 9AZ / Tel. 01 654 705950 / Fax. 01 654 702782 / email, info@cat.org.uk / website, www.cat.org.uk



Centre For
Alternative
Technology
Publications



Introduction

Greywater is all household wastewater except that from the toilet.
In the UK we each produce around 120 litres of greywater per
day, but if you're concerned about water use and take efficiency
measures (see 1 and 6 in resources below) this can be reduced to
around 30 litres per day. If this is the case, it may not be worth the
effort of creating a system to reuse this relatively small amount of
water; you would be better advised to collect and reuse rainwater
as this is cleaner and easier to do. Nonetheless, greywater is
produced all year round so you won't run short in the summer.
Although only around 6% of domestic water use is in the garden,
everyone wants to water their plants just as water reserves are at
their lowest: up to 70% of water demand on a summer evening
can be due to hose-pipes and sprinkler systems.

If you haven't got a mains sewer connection then you will
have to treat all of your greywater. The garden irrigation systems
outlined may help you achieve this, but you will need a default
treatment system as well. For details of permanent wastewater
treatment systems such as soakaways, filters or reedbeds read
'Sewage Solutions', and for alternatives to the flush toilet read
'Lifting the Lid' (see 2 and 4 below).

It is possible to clean greywater and reuse it for flushing toilets
in the house. Commercial systems are available to do this, but
so far they can only handle bathroom water, are expensive to
buy and use large amounts of energy. It is usually far 'greener'
and cheaper to spend money on other water saving measures or
collecting rainwater.

Making your garden water efficient

Before you start recycling greywater in the garden, make sure you
have taken steps to conserve water - allow more ground cover,
mulch your flower beds to reduce water loss and add organic
material to the soil to retain moisture. Fit a trigger nozzle to your
hose to reduce wastage, and install a rainwater butt.

How 'dirty' is your greywater?

Some of the things that make your greywater dirty, such as soaps,
shampoos, washing powder and cleaning agents may not be
good for your soil. Here are a few components that it is worth
being aware of:

• Sodium content - Using standard washing powders can be
the equivalent of throwing 90g of salt down the drain with every
wash. Although sodium is an essential nutrient, high doses
have a similar effect as drought stress on plants. Sodium is not
essential for cleaning and low sodium laundry detergents are
available.

• Phosphorous - Phosphorous is an essential nutrient and
shouldn't do any harm in your garden. But it is worth being
aware of its negative effect in ponds and waterways where it can
cause eutrophication.

• pH - Household cleaning chemicals tend to be very alkaline
(high pH). It is best not to water plants that prefer acidic soils
with greywater.

• Solids and fats - Greywater contains varying amounts of
organic solids such as skin and hair. Kitchen sink greywater



contains food, solids and greasy fats. These residues tend to
block pipework and should be taken into consideration.
■ Bacteria and other pathogens - Since greywater contains
bacteria and a nutrient source and is often discharged warm,
you have an ideal situation for pathogens to multiply.



Warning: do not store greywater! After 24 hours it will quickly
stagnate, become unpleasant to handle, and pose a health risk.



Which sources of greywater are worth recycling?

All greywater is potentially recyclable, with water from each use
having its particular merits and drawbacks. You will need to
consider the following:

• amount available (and how regular the supply is)

• quality (i.e. likelihood it contains contaminants and/or solids)

• ease of getting the water

• type of use to which the water is going to be put.

Kitchen water contains lots of solids and fats and is best filtered
before use. You may be better off collecting the waste nutrients
rather than water from the kitchen using a simple straw trap.
Laundry water may be high in sodium and detergents, so spread it
around the garden, rather than using it all in one place. Consider
using less detergent, or an alternative such as "Eco balls" (see
2 below). Don't use the washing machine's own pump to move
water uphill or around the garden as it will rapidly burn out.

Water from showers, baths and washbasins tends to be quite
abundant and is usually reasonably clean. For irrigation systems
the water from upstairs can be of more use as the height allows
the force of gravity to move the water further for you.

Reusing greywater: Direct application

Dirty water can be decanted directly from the washing-up bowl
onto suitable garden plants. This is efficient as you can target
particular areas and deliver appropriate doses. Pour the water
onto the soil, not the plants. Similarly, use your bath water for
house plants or fit a 'DroughtBuster' inline siphon pump to your
hose-pipe and run it from your bath out into your garden.



Wastewater pipe



The Straw Trap

Whatever your situation, there
is one simple thing you can
do to reduce pollution and
reclaim valuable nutrients: use
a straw trap. This is simply a
basket of straw or dry grass
inserted into your kitchen
drain. It will filter out coffee
grounds, food, some fats,
and other bits and bobs. It
also reduces the risk of your

drain getting blocked. From time to time, say once a fortnight,
remove the basket and dump its contents in the compost.
Then, simply fill with fresh straw and replace.




Drain



Less paper, more trees: download this tipsheet and other titles at www.cat.org.uk/catpubs



More complex approaches

Anything more advanced and you will need to get acquainted with
your plumbing, possibly separating your greywater waste pipes
from your main sewage soil-pipe.

Under sinks there will be an S-trap that contains water all the
time to isolate the sink from the outside drains. Then the pipe will
either go straight out through the wall or snake along a bit before
going through. Nip outside and take a look at where the pipe
comes out of the wall. Generally it will emerge in a 32mm
(1 %") or 40mm (1 1 / 2 ") pipe. On the ground floor it will go directly
into an open drain with a grille in it. This drain may also take
waste from pipes such as those removing water from a washing
machine, upstairs sinks or a bath, etc.

If you want to collect water from these pipes you will only be
able to do so if they emerge at a high enough level to drain into
a watering can or other vessel. You'll need to cut the existing
pipe(s) and insert a hose spigot, or something similar, along
with a flexible hose that can be put into the container. Ordinary
Vz garden hose is liable to clog, so it's advisable to fit a %" bore
flexible hose in your divert system.

If you have an upstairs toilet there will be a 110mm (3") vertical
soil-pipe to the sewer (either inside or outside the house), and
greywater from upstairs will join this pipe at a high level. If the
soil-pipe is outside it is simpler to capture greywater before it
enters. With an internal soil-pipe you will have to drill a hole
through the wall to pipe your greywater outside the house (so
consider carefully whether this would be a good use of your time
and money).

So now you've found the appropriate pipes, how do you use
the water? Remember that you should only store greywater for a
maximum of 24 hours. If you don't want to be watering the garden
365 days a year, then you will either have to have a continuous-
use system (as outlined below) or a system of capturing some of
the water when you want it and letting the rest run to the sewer.
There are valves available to help you do this, the 'Water-two', for
example (see 5 below). Before taking a shower or pulling the bath
plug you have to pop outside and pull a string on the valve and
change the flow direction away from the sewer and into a tank (or
watering can). Remember to reset the valve again afterwards.



t_ vent pipe




earth slope



Figure 1: Simple washbasin system
Source: The Water Book (CAT Publications)



Simple washbasin
system

Greywater from
washbasins can be
reused quite simply using
the system illustrated
(Figure 1). The outlet
pipe can potentially travel
any distance to a suitable
spot as long as it has a
2% slope. A more robust
solution is required for
the kitchen sink because
of the larger volumes of
water and the problems
of grease and solids
blocking pipes.



Whole house greywater system

To continuously collect and use greywater from large volume
sources like baths and washing machines you will need to install
a simple surge tank and filter, as illustrated (Figure 2). The tank
can act as a hopper combining flows from several sources if
required. It then temporarily stores water allowing your appliances
to drain quickly and the water to cool. The straw removes solids,
minimising the risk of blockages, and can be removed and
composted every few months. A 40 litre tank should be sufficient
for an average household.




straw



greywater out
Figure 2: Surge tank and filter
Source: The Water Book (CAT Publications)



Irrigation with greywater in

greywater

Since you don't want
to store greywater for
any length of time,
but use it straight
away, direct irrigation
of the garden is the
simplest solution
overall. On no
account should a
spray irrigation system
be used for untreated

greywater. Greywater should be applied below the surface to
minimise the possible risk of infection from contact with faecal
bacteria. What's needed is a system of perforated pipes running
through the the areas to be irrigated, allowing water to drip out
into the soil. Your flowers and vegetables will thrive on it.

Commercial drip-irrigation pipes will quickly become clogged
with greywater impurities, so you'll have to make your own. You
can use a hose-pipe pierced with holes (3mm holes every 20cm)
or plastic waste pipe (32mm/40mm, with 8mm holes every 30cm).

Water pressure will drop along the length of the pipe so it's
better to have a system of branched pipes rather than one long
snake. With branches you can also install isolating taps to direct
the greywater where it's most needed. The end of each pipe
branch should have a stopper to improve distribution. This can be
removed periodically and the system flushed thorough to clear out
any blockages.

Better distribution is achieved with less likelihood of blockages
when pipes are laid in a trench full of woodchip next to your plants
(10-20cm deep), rather than directly in the soil. The woodchip will
break down and compost and will need replacing every two years.
More details can be found in Judith Thornton's The Water Book
from CAT Publications (see below).

Finally, some legalities: don't run tap water down your irrigation
system unless you have the required 'Type DB device' backflow
prevention.

Conclusion

Greywater reuse is far more complex and problematic than
you might at first expect. Unless you are particularly keen, we
recommend you use greywater only for garden irrigation and only
if the simple, cheap systems outlined above fit your particular
situation. Finally, it is not recommended that you dilute your
greywater with rainwater; it is better to use these two supplies
seperately. Plus, greywater will not store safely any longer than
24 hours even when diluted.



Notes & further information

1. Water Conservation, CAT tipsheet

2. Sewage Solutions: answering the call of nature,
Grant, Moodie and Weedon, CAT Publications

3. Reedbeds and Constructed Wetlands, CAT tipsheet

4. Lifting the Lid: An ecological approach to toilet systems,
Harper and Halestrap, CAT Publications

5. 'Water-two' Valve

tel. 01539 623429 www.watertwo.co.uk

6. The Water book: find it, move it, store it, clean it. ..use it,
Thornton, CAT Publications

7. Create an Oasis with Greywater,
Ludwig, Poor Richards Press

8. www.oasisdesign.net American site with wealth of
information on greywater use in the garden

The above titles are available direct from CAT Mail Order - tel.
01654 705959 to order or receive the complete Buy Green By
Mail catalogue. Visit www.cat.org.uk/catpubs to order, read
reviews or download tipsheets and factsheets.



© The Centre for Alternative Technology, 1998, updated 2006. Published by CAT Publications, CAT Charity Ltd. Registered charity no. 265239