Wednesday, 28 January 2009

water - carbon cost

While working out my carbon footprint earlier this month I also mentioned my annual water consumption, and started pondering the carbon cost of water. I emailed South West Water, the water company for Cornwall and Devon, and fairly soon after received a reply from their Carbon Manager David Rose (impressive they have a dedicated Carbon Manager but apparently many similar companies do now).

Clean water delivered: 173 grams CO2e per cubic metre of water delivered to your tap.
Waste water returned: 870 grams CO2e per cubic metre of waste water returned to sewer.

(CO2e = carbon dioxide equivalent)

This equates to 1043 grams CO2e per 1000 litres for combined clean and waste water supply - I have to admit to surprise for the low delivery figure for fresh water. But then, water arrives freely from the skies. It doesn't (here anyway) need to be pumped up from the ground.

If there is a message to be read from these figures it's that the less 'contaminants' we put into the waste/sewer the lower their clean-up costs, and this might help lower emissions. David explained that the waste figure includes methane and nitrous oxide emissions from the recycling of waste water sludge to land. Or muck spreading as I've always known it.

My household carbon contribution from water use then is:

34,527 litres
= 34.527 cubic metres x 1043 grams
= 36011.661 grams CO2e
= 36 kg CO2e pa

Thirty-six kilograms, or 0.036 tonnes, sounds not very much in comparison to other emission costs, such as heating water or travel. So it seems best to retain focus on reducing quantity of water due to its eminent predicted global shortage.

So, over the next year I should aim to reduce consumption, and consider what gets disposed down the mains that needn't and other options for disposing of it (or do away with it altogether?).

Emission levels from all UK water companies are shown in Figure 4 on page 12 in Water UK's Sustainability Indicators 2007-08 Report.

United Utilities have a user friendly (figure-phobic) water use/carbon calculator here but be aware the final figure includes not just the carbon cost of water supplied/taken away but the carbon cost of heating it.

Update 14 February 2009
South West Water have announced plans to trial a rising block tariff. There will be three blocks, the first low rate 'essential use', the second standard rate 'safety net' and third premium 'non-essential use', with the first block charged at 27% less than the standard rate.

For a one person household the essential band is 1-8 cubic metres/quarter, the standard 9-13, and premium 14 and over. So I'm thrilled to see that my existing quarterly use only just flips over the essential use level!


Quail said...

Owning a house means that for the first time I can harvest rainwater by using waterbutts. Living in Devon, there's plenty of rain! I use the water I collect for my business. I rinse starches out of my fabrics in a bathtub, water house plants and water plants all over the garden. The house plants seem to be the healthiest they've ever been...I have about 30 of them!

Stephie said...

I rent a property and am apprehensive about asking if I can install a waterbutt as the downpipe is on the front of the house. A previous tenant was given permission to insall a satelite dish at the back of the house and the landlady says she regrets it! I use grey water for watering the garden and my flower pots though. I am lucky enough to be on a water meter here though, so I can see how much water I actually use. At the moment it's looking like about 40 cubic meters p.a. (I haven't been here a full year yet), which I don't think is too bad considering there are two of us here most of the time? The main problem I have at the moment is getting my 10 year old son to turn the lights off when he's finished with them!

Robin Paris said...

Hi Steph and Quail (Shauna) and thank you. You're right to bring up the topic of rainwater harvesting... it had slipped my mind in this post I think because I was focusing so much on the SWW and carbon issue.

In a post long ago I did mention that collecting rainwater off my roof is an ambition, for work purposes (rinsing, dyeing whatever) but until I move house/studio is not really practical. I live central terrace and the communal back path prevents having a butt directly by the house. In my mind I have designed one that reaches out across the path and down into my garden (and similar from the bathroom), but I can see it getting damaged as soon as a ladder comes this way, or when the February gales blow. And it would look weird. At the front is practical but aesthetically insulting to such a traditional terrace.

I do collect rainwater off the shed roof for watering the garden - not needed too often because of the amount of rain here on the moor! The shed butt is 90 feet up the garden - I don't feel inclined to carry water from there to the house to use for work. Perhaps I should.

Steph, couldn't you collect rainwater off your shed roof? Landlady can hardly complain at that!

Shauna - have briefly dropped in to your blog and look forward to a longer visit soon!

Stephie said...

Unfortunately, my 'shed' is more of a stone built outhouse attached to the FRONT of the building - it's even got plastered internal walls! I'm trying to pluck up the courage and ask though...

Any news about a possible house move your end?