watering system

Our heads hurt!  We are trying to design our grey water system and it’s making our brains ache…  The principle of re-using waste water from showers and sinks is a fantastic one but there is SO much involved in getting it right.  Here’s what we are getting our heads around…

Once the water has drained through a series of filters (a grease trap, a sand filter and a series of cascades planted with reeds etc) it will trickle into pipes directly into some of our raised beds.  The pipes must be sunk 10cm into the soil - this is because the micro-biological action needed to process the grey water happens at that depth plus we don’t want waste water sitting on top of the soil and causing a smell or a health hazard.  Not all of the beds will be fed by the grey water system – root veg form their fruit under the soil so it’s best to use clean water to irrigate them.  The last bed in the run will get the most water and this is where we will plant tomatoes, peppers, cucumbers & courgettes as they will thrive on lots of water and become plump and juicy.

Yesterday we spent an hour at the local plumbing supply shop sourcing enough bits for the irrigation system for 1 raised bed.  The guy there speaks excellent English and is really friendly.  He’s come to know us pretty well now and listens with patience to our strange and complicated requests.  He commented yesterday that he was thinking of opening a factory called ‘Steve’s designs’ to make all the odd bits and bobs we need!  Here’s Steve assembling all the bits of pipe on our terrace, looking like his head is about to explode with all that thinking (it’s sunny and he’s just squinting, honest!):

The main pipe that flows from the filters plus the pipes that feed 4 of the 6 beds will act as a reservoir.  Luckily there is someone in this household that does maths – as I type Steve is calculating the volume of water that will be contained in all these pipes.  Once we know this, we then have to calculate the volume of water if all the showers and sinks are being used simultaneously (ouch!  more maths!).  The difference between what the system can contain and what might be discharged will then tell us how big our ’surge tank’ needs to be – so that the waste water never backs up.

Other variables include: the gradient of the pipe (needs to be sloped enough for the water to flow via gravity but not so steep that it gushes out and doesn’t irrigate along the way – 2% is the recommended gradient); the size of the holes in the pipes buried in the beds (big enough to let the water flow out at a reasonable rate but smaller than the gravel we’ll use around the pipe); the number of holes in each pipe (spaced enough so that all areas of the beds get water but not so many that soggy patches emerge – we’re into total guess work now!!) and finally the type of soil being irrigated – ours is clay at lower levels with a good depth of top soil.  We’ve decided to go for drilling 3mm holes spaced 20cm apart.  We’ll pour some water in and see what the flow rate is and maybe adjust.  Here’s Steve drilling holes into the pipe (you can see how hot it is today but notice the terrace is still wet from the last downpour – proper April showers!!):

We are resigned to this year being all about trial and error.  Watch this space to see whether we manage to design our filtering tanks and cascades from recycled materials or not; whether our system floods or backs up and whether our vegetables grow, die or swim!