2 Apr 2009

Thin line between wonder products and cons

I am stirred to write by some correspondence I have been having with Nick Grant, a water maven and a leading light in the AECB. Nick has recently come out against rainwater harvesting (RWH). He now reckons it’s a complete waste of time and energy and lists no less than eight reasons why you should avoid it. These being:

1. Very cost ineffective — about £15/m3 life cost for RWH assuming pump doesn't fail after 2 years. (By way of comparison, mains water costs around £2/m3.)

2. Doesn't save enough water to be meaningful, and can't be installed in enough places.

3. Doesn't work where needed. Thames gateway — no roof area/person, nor rainfall, even less in a dry year when needed to save water.

4. Can fail, leading to mains top-up running to waste and so undoing all the savings that could ever have been made.

5. Problems flushing loos when power off or pump broken

6. Uses 2-4 times the energy of mains, but still only a little compared with water heating. However that debunks the idea that all houses should have RWH to save all the CO2 needed for pumping mains.

7. “Ah but what about all the chemicals and other environmental impacts.” Again, argument needs to be that rain is significantly better than mains to justify the green premium, but is actually worse.

8. “Ah but I want to save water, but don't want a low flow shower” (perhaps meet CSH 3).

He is not alone. There is a considerable weight of opinion gathering to dis rainwater harvesting as a green con. I am not so sure, but then I don’t know that much about it. But it strikes me that there is now a fairly long list of supposedly eco-products out there that have been slated for being worthless. I can think of:

• multifoil insulation
• polyurethane foam insulation sprayed under roofs
• micro wind turbines
• electric heat pumps
• green electricity tariffs
• magic energy savings devices (as made by EPS who have a very strange website indeed
• green roofs

And then there are products which some people advocate, whilst others think are a complete waste of time. Think maybe limecrete. Or hemp. Or biomass boilers. Or micro-CHP. Or perhaps triple glazing. Or even mechanical ventilation with heat recovery.

I have no doubt that people making and selling these products don’t start out to con anyone but that, quite naturally, they sell their good points and ignore the bad ones. Any visitor to Ecobuild can’t have failed to notice that every single exhibitor trumpeted their green credentials — and why not? But logically, some products must be greener than others. Thus far any attempts at producing an authoritative overview — such as the BRE’s Green Guide — just produce howls of protest from people who don’t like what they see there.

It makes it all very hard for the consumer to make sensible choices. And I can’t see it getting any better, as more and more green products arrive in the market place and there are no agreed systems for testing their claims. Seeing as the government has been offering grants for some of these dubious products, and including others in its Code for Sustainable Homes, what hope is there for us mere mortals to make sense of any of it?


  1. I think the issue is that any of those products you mentioned do actually perform as intented, and are actually green, BUT only when used in the right circumstances in the right area, with the right detailing, and where applicable with the right locally sourced materials.

    look at any of these products without considering these variences and you'll be able to start poking plenty of holes in them, i can't see any way of providing a workable "green certificate" system, it just seems like to much of a gargantuan task.

  2. Rainwater harvesting never made sense in the North or the West of the country, we have plenty of water. Clients that have installed systems have had problems with pumps and blockages and would certainly not use them again.

  3. Got to agree with this. "Green Wash" is actually putting people off being eco-friendly!

  4. Mark,
    I would like to see your thinking articulated more clearly on why you think mechanical ventilation with heat recovery may be a 'waste of time'. Having just installed one in our near passivhaus standard refurb. (a victorian solid walled house), and having just embarked on gaining first hand experience of living with this piece of kit - I would be interested in what views you have developed and how you arrived at them. I will certainly let you know - in due course - what I think as a result of our little experiment....
    Andy Simmonds

  5. Andy,

    I am not actually saying that MVHR is a waste of time. But I have expressed doubts about its effectiveness when rolled out across the population at large, rather than being installed by enthusiasts like yourself. Here:


  6. Hi Mark

    For the record I was quoting Judith Thornton’s excellent presentation at Ecobuild but I stand by all the points myself even if I can’t claim full credit for pulling them together.

    I have known about the issues with rainwater for some time but have kept quiet unless asked as I have friends who sell the kit. As Judith said in her presentation, we make uneconomic decisions every day and that is fine but the CSH and planning requirements are forcing people to make economically and environmentally unwise decisions and that is ethically suspect and a serious hindrance in terms of actually tackling the real issues of water shortage and climate change.

    As Prof Bob Lowe said ‘the most dangerous problems are the ones that you think you have solved. Anything that makes you think you have solved a problem that in fact you haven’t is therefore to be avoided at all costs’.

    I’m currently pro MVHR, with caveats, but then I was arguing for rainwater once.

    I do however think that laypeople can and should do the basic numbers themselves, typically the stuff that really doesn't make sense it pretty obvious once you adopt a critical (not cynical) approach.

    Bullshit detection really should be taught in schools, perhaps as part of RE. Anyone I havent offended?


  7. Mark, I really don't understand your reluctance to embrace MHRV systems. Where I live, they're required by code. Of course, if you're not building airtight, then it is a waste of time. I think maybe the problem is you seem to be conflating the function of ventilation with heating - MHRV systems are not normally used for heat distribution as the airflow is not sufficient.

    As for your list of other products that are cons, I'm surprised you mention heatpumps as something that "does not work". What is it about heatpumps that does not work in your mind? Maybe they're being oversold in a UK context as a "low carbon" solution, but eventually the UK will not be in a position to burn natural gas for heating.


  8. Paul,

    I can only reiterate what I wrote in my answer to Nick about MVHR. I am not dissing heat pumps, merely pointing out that you will hear some people being very rude about them, and suggesting that they are a con. It's not my line.

    I suspect that one day not too soon electricity will be the only fuel we can use and then heat pumps will be everywhere.

  9. Interesting article about heat pumps in the Telegraph which concurs with your view that the UK hasn't used them in quantity due to the cheap gas and oil.

    See link here

  10. If anyone is interested then I've made available a spreadsheet I developed as part of my PhD thesis which looked at the cost performance of rainwater harvesting systems. I'm not sure I can post links here but if you Google for "RainCycle" it will come up at or near the top of the list. The spreadsheet can be used to assess the water and cost saving potential of rainwater systems.

    Richard Roebuck

  11. archess200July 15, 2010

    What's all this about rainwater recycling not being cost-effective? If you lived in the west country with highet water bills in the world, you would soon notice the difference. We have had a 1000 l tank at the top of our garden drip feeding our wc for the last 4 years. It was a free tank (exchanged for an MOT failure) and the plumbing bits we had around. It's slow, needs more head, but our water bill is about £100 per year. I am economical with water anyway, but it should be about £1000 for the 2 of us. The biggest saving is on the cost of the waste charges, which of course are not metered if you are using your own water. How long before they catch on with that one?

    Now looking at new build with big big tanks in the basement. For £3000 for life, as long as you can fix your own pumps, that suits me.