Saturday 22 September 2012

Water Management

When I purchased my plot of land in Crete I did so with the objective of being able to live off-grid using the natural resources to meet my needs. I therefore ensured that the plot I purchased (see earlier post "Finding a Plot) not only had sufficient space to allow excellent solar access to the abundant Cretan sunshine but also its own source of spring water. Over the last couple of years I have been monitoring the flow of water, whenever I have visited Crete and, although I have yet to be there in August, the spring has continued to flow albeit at a slower rate in the summer months. The water has been analysed and although, unfortunately, not another Evian or Volvic it is of drinking quality with:

Our water supply
pH            7.65       (6.5 - 8.5)

Cl           53 ppm  (< 250 ppm)

NO3         3 ppm  (< 10 ppm)

SO4     106 ppm  (< 250 ppm)

There is already a small storage tank holding approximately 12,000-15,000 litres that was previously used for infrequently watering a small number of fruit trees and a large crop of artichokes ( a local delicacy when served raw with salt and lemon and accompanied by chilled locally brewed raki).

Existing tank under construction
In mid May last year (2011) I was living on the plot ("camping" in the shepherds hut on site) for a couple of weeks and used the time to observe the plot closely and for example to record daily the rate of overflow from the storage tank which was overflowing after the winter rains. I took a sample at the same time each day and recorded the length of time (using a stopwatch) for the overflow water to fill a 20 litre bucket. From these results I calculated that the flow rate over the two week period was between 5000 and 6000 litres per day. Even allowing for experimental error and the fact that it was late spring, when you would expect the flow to be at its maximum, with the snow melt on the mountains in progress, this flow should easily enable an additional water storage reservoir to be filled. The existing storage tank would then be used to irrigate an extended orchard and forest garden interplanting (see later posts).

I have noticed over the last couple of years that in addition to the water already flowing into the existing storage tank there may well be additional water seepage through the soil at a level lower from the tank.  I will examine this possibility at a later date since the installation of a suitable spring box  or seep collection system could well capture this water for irrigation purposes. Will address this in a later post.

Next year's water supply!!

Water Consumption

Given the off grid nature of the plot I was concerned, from the outset, that water consumption of the house needed to be minimised. I therefore investigated and researched using grey water (ie washing machine, dishwasher, shower etc water) for garden irrigation after passing through a reed system and collecting and storing rainwater. Having discussed the reed bed concept with local engineers I decided to abandon re-using the grey water as, given the long, hot dry summers in Crete there was a high risk of the reed beds drying up and the reeds dying.

Average water consumption in UK households is estimated to be 150 litres per person per day with an initiative to be 120 litres per person per day by 2030.

From "Green Building Bible Vol 2" (an excellent reference volume)

- Toilet flushing accounts for 30%
- Washing and Hygiene        40%
- Laundry                              12%
- Washing Dishes                   6%
- Drinking and Cooking           2%
- Gardening                            4%
- Miscellaneous                      6%

Using the latest water saving devices (toilet flushing, shower heads, AAA rated washing machine and dishwasher etc I estimated that this could be reduced considerably (by up to a half with the best water saving devices).

However, given the long term aim to develop a forest garden on the site, the above gardening requirement would need to be considerably increased. Therefore, I estimated, allowing the full 150 litres per person per day for our two person household would allow for the extra garden requirement and occasional visitors in the summer period.

Therefore estimated requirement for the house and garden is currently 300 litres per day.

Water Storage

Assuming a worst case scenario, with continued global warming, ideally require a six month storage capacity. ie 300 x 180 = 54,000 litres.

The current plan, therefore, is to incorporate a 60,000 litre concrete storage tank (6m x 4m x 2.5m) into a carport/storage shed facility that will have the solar photovoltaic array on the roof (see later post).

Given the flow data detailed above further water storage will be added, as required, at a later date.

With regard to rainwater, given the earth sheltered design of the house, the initial approach is to install a drainage pipe at ground level at the bottom of the east, north and west walls before they are covered in earth and running them to outlets on the southern side of the house at both the west and east side. From experience will then decide whether this water should be stored in underground tanks or simply drained to irrigate the garden below the house.

Waste Water Management

Prototype composting toilet
Given the problem with re-using greywater (see above), and after fully researching composting toilets (including constructing and using a prototype version whilst camping on the plot) and separator systems together with the low level of water flow in the waste systems (due to latest water saving cisterns) the general consensus of opinion from research, and talking to engineers, is to use a septic tank or cess pit system for  all waste water, except rainwater, with herringbone drains to run off across the lower garden.