Getting rid of greywater in a small garden

Reusing greywater is the first half of this and covers what it is, which sources are safe for what, and the 24 hour rule. This page is the other half: what to do with the water you cannot use, in a small garden, when the drains have stopped taking it.

The volume problem

A household using water carefully still produces a great deal of it. Washing bodies, washing clothes, washing up and cleaning generate well over a hundred litres a day for a family, even under rationing.

That has to go somewhere. If the mains drainage has failed, or you are on a septic tank you are trying not to overload, the garden is the destination, and a typical British plot is smaller and wetter than people assume.

The failure mode is not dramatic, it is gradual: one patch of ground gets everything, it saturates, it stops absorbing, water stands, it goes anaerobic, it smells, it breeds insects, and it becomes a place children and animals walk through.

Use it before you dispose of it

Every litre used for something is a litre you do not have to dispose of, so the reuse page is also the disposal strategy.

In priority order:

1. Flushing the toilet, which is the single largest sink for greywater and needs no quality at all.
2. Watering non-food plants, hedges, trees, lawn and ornamentals.
3. Watering food plants at the soil, from bathroom and laundry sources only, never kitchen.
4. Cleaning: floors, boots, tools, the yard.
5. Then disposal, for whatever is left.

In a dry summer this problem disappears entirely, because the garden wants all of it. The problem is a wet British winter, when nothing needs watering and the ground is already saturated.

Where it must never go

Spreading it

The whole technique is distribution: many places, a little at a time, rather than one place repeatedly.

• Rotate the disposal point every day or two. Mark them if you have to.
• Under trees and hedges is the best destination. Deep roots, high demand, no food crop, and the soil under an established tree absorbs far more than open lawn.
• Onto mulched ground, not bare soil. A thick mulch of wood chip, straw or leaves absorbs the water, filters it, and stops it running off or capping the surface.
• Never in the same spot twice in a week in winter.
• Strain out solids first. A cloth or a mesh over the bucket. Food particles and lint are what cause smell and clogging.
• Cool it if it is hot. Very hot water damages soil life and plant roots.
• Spread thin and wide, not poured in one place. A watering can with a rose beats tipping a bucket.

Keep detergent low. The sodium point on the greywater reuse page applies to disposal too: sodium accumulates, destroys soil structure, and turns a workable bed into something that sets hard and drains badly. Low-sodium, low-phosphate detergent, used sparingly, is the difference between improving the ground and ruining it.

A simple soakaway

For a fixed disposal point that can take regular volume.

1. Dig a pit, roughly a metre cube, well away from the house foundations, any watercourse and any water supply.
2. Fill it with coarse rubble, broken brick, stone or gravel.
3. Cover with a layer of gravel, then a permeable membrane or a thick layer of straw, then soil or a removable lid.
4. Deliver water onto it through a strainer, so solids never reach the rubble.
5. Plant something thirsty near it: willow, comfrey, a hedge.

Test your soil first. Dig a hole, fill it with water, and see how fast it drains. If it stands overnight, you have clay or a high water table and a soakaway will not work; you need spreading instead.

How much ground it actually needs

The page has given a volume and a set of rules and never put them together, and the arithmetic is what makes the winter section below unavoidable rather than merely cautious.

Take the page's own two constraints: a family produces well over 100 litres a day, and no spot gets used twice in a week.

A small British garden does not have thirty spreading points, and that is the finding. It is not a matter of effort or technique: the ground is simply not there.

Which is why the priority order at the top of this page is not a preference, it is the answer. Every litre that goes down the toilet is a litre that never needs a spreading point, and flushing is the only destination whose capacity does not depend on the weather or the soil.

The consequences, in order:

1. Flushing takes as much as it possibly can, particularly in winter. This is the single largest lever.
2. Reduce production. Water used twice before it becomes waste halves the disposal problem, and in winter that discipline matters more than any technique here.
3. Under trees and hedges absorbs several times what open lawn does, so the few good points you have are worth using properly.
4. A soakaway concentrates the problem in one place, which is efficient in summer and is exactly the wrong shape in winter.
5. Then accept a smaller volume. If the ground will not take it, the answer is to produce less rather than to force it.

Test your own ground before you plan around it. Dig a hole a spade deep, fill it with water, and time it. That single measurement tells you whether spreading or a soakaway is realistic on your plot, and it gives a completely different answer in January from the one it gives in August.

Winter, when the ground stops taking it

The honest constraint, and the reason this page exists.

In a wet British winter the ground is already at capacity. Rain has saturated it, plants are dormant and taking up nothing, and evaporation is minimal. A soakaway that coped in August will refuse in January.

What actually helps:

• Produce less. Winter is when water discipline matters most, because disposal is hardest. Shorter washes, fewer loads, reuse water through several jobs before it becomes waste.
• Prioritise flushing. It is the one destination that does not depend on ground conditions at all, and in winter it should take nearly everything.
• Use hard standing carefully. A yard that drains to a foul drain, if you have one, is a legitimate route.
• Multiple spreading points, further apart, rotated more slowly.
• Under evergreen hedges and conifers, which stay somewhat active and shed rain, so the ground beneath is drier than open ground.
• Accept a smaller volume, and adjust behaviour rather than trying to force the ground to take more.

If it is standing and smelling, stop putting water there immediately and let it recover. Continuing is how a small problem becomes a permanently sour patch of ground.