Scaling water interventions

Conversation with someone chatting to me after the UCT water crisis lecture today (by the way, this Future Water page has many interviews and chats about the crisis, in balances informed tones). I didn’t go. Was duckfood shopping with a brief stop to do retail therapy. (The stress to submit the thesis has caused insomnia and to get myself to fall asleep I have been watching, wait for it, nail art videos.) So I went buying nail art stuff. Yup. Glitterified.)

Neil’s been working on sustainable urban water management for a long time. – http://www.uwm.uct.ac.za/
His comment about the rainwater tanks (being: rain tanks are a waste of money for the amount of buffering they provide) comes from his PhD student Lloyd Fischer- Jeffes’s work, where they saw that rainwater is more expensive than stormwater harvesting and managed aquifer recharge – which is effectively a huuuuuuge rainwater tank underneath the city.

[another UCT researcher said “imagine if 1/2 a million people had 2000 litre rain tanks, that would be 1000 million litres of water buffered. ]

1000 million litres is two days of CT’s water supply under level 6 restrictions (Is my math correct here?). We get about 6 storms a year, so let’s say we multiply that by 6, gives 12 days of buffering. That’s a lot of effort for not much return. I do think we should encourage rainwater tanks because it’s an easy way to get people to understand their water use and visualise how much they’re using. From comments on FaceBook, this also holds more for a city than for way-out places, where the costs of getting the water there is different, and water security looks a bit different, perhaps.

If you think of the cost of a rainwater tank of 2 000L, what’s that, R5000? multiplied by 500 000 = R2.5 billion? That’s a lot of money for 12 days buffering, think we can do better.

Neil also said something else the other day – someone said we need dual piping to our homes with treated wastewater to flush the toilets. That’s a large cost for the extra set of pipes. There’s also risk of that water potentially being in contact with people, and cleaning wastewater to potable level is cheaper. But, Neil reminded us that the city is actually treating wastewater and reintroducing it into the system, and has done so for a while. This effectively achieves the same as the dual pipes would, for much cheaper. Of course, on the other hand this requires functioning infrastructure, good governance and institutional competence. As a city, we are doing OK with that, but we don’t trust the powers that be.

*** But this begs the question, if we have a certain amount of effort & resources to spend, should that go into innovations that is the equivalent of rainwater tanks, or should we rather work on improving the governance and institutions managing these things? ***

There’s a reason the world is urbanising. It’s more efficient. What we need to learn is how to apply this efficiency also in taking care of our environment and out social structures.

2 Replies to “Scaling water interventions”

  1. In Cape Town, based on meteonorm’s ten year typical data set: it rains every 3-5 days for most of the year and every 5-10 days in January and February. That’s a lot more rainfall incidents than 6.

    Acknowledging raonfall volumes and collection area, I worked out that a 2000 l tank rigged up to supply our dishwasher, washing machine and toilets can provide at least 50% of our water needs for about 60-70% of the year. That’s a lot more than 12 days buffering.

    1. Thanks Peta. Not each of those incidents would fill the tank up, which is why I used the ‘6’ – as in proper storms that would fill it up completely. but there is the CSAG tool – http://cip.csag.uct.ac.za/webclient2/waterharvest/ which helps to calculate all of this.

      From discussions with friends we acknowledge that there is both a social and an economic component to this. Socially, feeling more water secure is important, and seeing how much water you have and how that changes as you use it, is important too. Economically what is the payback time for one’s rainwater tank as compared to the water usage rates? Then I guess there’s also questions about the city’s income as it is currently structured. Would the city be willing to subsidise rainwater tanks for lower incomes if that action takes away their income? Where would the money for the subsidy come from? I don’t know the answers…

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