Are filters necessary?

At the moment, when we're camping on our site, we just throw our basins of water into the rushes and let the willows and alders deal with it. When we build our house do we need a special greywater system with filters or can we just run the water to an area planted with willows and alders?

Hi Autumn, two things: environmental protection, legal obligation.

To make sure you protect the environment, if the soil conditions are ok then you may be fine routing the grey water to the willow and alder patch. Even an information open wetland area may be sufficient to contain ALL of the effluent until it filters down through the tree roots. However, if you get runoff from this area, chances are it won't be nice for the local stream. If you get infiltration into the ground and there isn't enough depth of dry suitable soil, chances are it won't be nice for the groundwater.

Hence a filter of some sort. That needn't be sand though. It can be a constructed wetland, a gravel reed bed, a comfrey bed designed for both infiltration and nutrient capture… there's lots of options (www.wetlandsystems.ie/watertips shows more examples).

Legal obligation is an important consideration. Typically the aim of this is for environmental protection, so don't be too afraid to find out what codes you need to meet. This may be of some help if you haven't seen it already. If you don't meet the relevant codes you may be asked to undo hard work and may even be prosecuted, so do take care to find out what's needed, and to implement it. You needn't follow the most expensive option - just know what is required, that's all.
http://www.sepa.org.uk/about_us/publications/guidance/ppgs.aspx
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/290141/pmho0706bjgl-e-e.pdf

Does that answer the question you have at all?

It's an extremely wet area, uphill from the septic tank. We were planning to plant willows and alders to try soaking up some of the water. If comfrey will grow in peat we'd happily use it.
Thanks I'll have a look at that link.

Very wet is a problem for percolation systems because the dry soil that does a lot of the filtering just doesn't do what it should, and you can get groundwater pollution or surface pollution of streams or lakes if you're not careful. I'd recommend some form of wetland filter before the willow/alder area to be sure. Have a look on www.wetlandsystems.ie if you want a bit of background information on those.

Comfrey should grow on wet peat if it is kept weed free initially and if there are enough nutrients to get it started.

Whatever system you build - make sure it's big enough. There's a list of common building mistakes that I can email you if you like. I'm at reeds@wetlandsystems.ie

Thank you very much Feidhlim. I will email you for that list.
We have various very wet bits, extremely dry (almost pure sand and gravel) bits and in between bits as well. I just assumed the wetter the better

I haven't yet been able to find anything about comfrey beds designed for infiltration and nutrient capture but I will continue to look, since it sounds as though it could be the perfect option for us.

Hi Autumn, wetter soils aren't necessarily better for sewage treatment purposes at all. It's the bacteria in dry soils that provides a lot of the filtration effect in a percolation area. If your soil is wet, then you'll need to consider putting in a well laid out wetland area or reed bed or something to get the water clean before the willow/alder grove. Grey water is surprisingly hard to filter, since the surfactants are hard to get out of the water again. Stop using surfactants and your grey water will be clean in no time - but that's not always an easy option, so most people would rather put in a filter (aka, constructed wetland or reed bed in this case).

Comfrey beds… what I recommend here is to follow the local guidance for your soil type and liquid volumes and set out a percolation area of that size. Then plant between the percolation trenches with Bocking 14 or other big comfrey species and let them drop their roots down into the soil. They'll take up N, P and K, and you can do about 3 harvests a year of the leaves. If you use something other than the sterile Bocking 14 you may get weeds aplenty; but that may or not matter to you. There are UK suppliers if you go looking. The roots come as tiny chunks of root which you then pot up, nurture and eventually plant out into the final positions. Comfrey is easy to propagate, so if you start small and care for the plants you'll have enough in a few years. I did this recently on a propagation bed, but didn't tend it enough and lost the lot. Have to reorder and start again.

I'm sure there are Scottish codes. If you're having difficulty let me know and I'll see if I can root them out.

Thank you Feidhlim. We'll use one of the drier areas and follow your advice.
We have the non-sterile comfrey, so, as you can imagine, we have no shortage of it
Hopefully I should be able to find the Scottish codes somewhere. If not, I'm sure SEPA would give me the information if I asked.

Best of luck with that work Autumn. You have my email address, so please feel free to email if you have questions.

Thank you Feidhlim. You've been a great help already.

It's been fun. It's actually my first time on Permies.com and I'm loving it. Cassie invited me for the US launch of the new book.