Dependable Erection

Monday, March 17, 2008

24,000 gallons a month?

Kevin discusses some of the implications of a paper presented by Duke student Wichsinee Wibulpolprasert, which analyzed a month's worth of water usage data from summer of 2007 and came to some interesting conclusions.

While both the paper, and Kevin's post, focus on the conclusion that new homes use more water than older homes, presumably because the new landscaping requires more irrigation than established landscaping, there were other, more interesting data presented.

It certainly appears from that graph that water use is strongly correlated to household income, more strongly than with the age of the house. According to the study, census blocks with 40% - 60% of houses built within the past 8 years used more water than blocks with 60% - 80% new construction, and blocks with 0 - 20% new contruction used slightly more water than blocks with 20% - 40% new construction.

But water use rose in all cases in lockstep with income increases, culminating in an 85% increase in water use between the $40,000 - 60,000/year category, and the $80,000 - 100,000 year category, from 12,700 gallons per month, to 23,300 gallons per month.

At all income levels, though, water use according to this study was absolutely astounding. Households with income below $20,000, for instance, are still using 9,000 gallons of water per month, or 24 units during a 2 month billing cycle. At the highest income levels, we're looking at a whopping 63 units for a two month cycle.

I'm really curious to hear from the city if these numbers, even leaving out the demographic information regarding household income, sound right. How many of Durham's households are using less than 10 units per billing cycle? How many are using more than 60? That might help answer the question of just how much are those of using minimal amounts of water subsidizing the wastefulness of our fellow citizens. And provide some good guidelines for how a tiered water rate system might be structured.



  • Interesting. I wish they'd use per capita figures instead of per household, especially since household sizes are typically smaller in the higher income brackets (which would indicate an even greater usage disparity). Also, where's the $60k-$80k bracket?

    Our household is small (only 2 of us), but we only manage to gulp down 10 units per billing cycle despite having ancient toilets and appliances. I don't even know what these people could possibly be doing to use so much, unless they're blatantly violating the current usage restrictions.

    By Blogger Jeremy T, at 3:10 PM  

  • the study only looked at data from july 1007, before restrictions were in place. so there's no violations to look at. I'm hoping that when Durham gets around to modernizing its billing system for water and sewer, that kind of info will be available in a more useful time frame.

    By Blogger Barry, at 3:17 PM  

  • Ah, well my lack of reading comprehension explains that.

    This makes me wonder what effect a tiered pricing structure would really have - if the people using the most water are also the richest, you'd need some *really* steep surcharges for them to even care.

    By Blogger Jeremy T, at 3:39 PM  

  • Yeah, the data doesn't make much sense at all to me. I was wondering if it's possible that those figures are cumulative rather than average, but the numbers don't work out that way, either.

    And if it is actually an average use of 24000 gal/mo, what in the hell are these people doing?? Refilling their swimming pools every morning? And what about people with am income over $100k? Maybe with a sample size of 5000, none of those showed up, but we have plenty of them in this area.

    By Anonymous Anonymous, at 4:10 PM  

  • I'm thinking that since there was only one month of billing data supplied, and Durham is on a two month billing cycle, that maybe the raw data was misinterpreted, and should refer to billing cycle use, and not monthly use?

    Not really sure if that's the case, but it might make sense.

    Also - Jeremy, i'm thinking, yes, really steep surcharges. A base rate for the encouraged level of usage. Triple that for the next tier. then triple the rate again for the "excessive" users.

    Two things to consider.

    One, water is actually the least significant part of the water bill, especially if you're a low level user.

    Second, setting the levels at which the different tiered pricing would kick in is going to be a political nightmare. If your do it based on previous year's usage (requiring everyone to conserve by the same percentage) then you're rewarding people who did nothing to conserve by giving them a higher allotment. If you set a baseline that is flat per household, then you're punishing people who might be caring for elder parents, or who have 4 or 5 kids. If you try to set a baseline using the number of people per household, then you could get into all kinds of privacy issues.

    I've noted before, when i lived in the drought-stricken Central Valley in the early 90s, allotments of water were based on previous years' use. We bought a house that had sat vacant for that year, so our allotment was 0. As part of the appeals process to get our allotment raised to a usable number, we had to sign an affidavit declaring how many people we had living in our house.

    I don't know how well that will go over in Durham.

    By Blogger Barry, at 4:22 PM  

  • Housing code regulates the number of unrelated people living in a house, and I haven't heard anyone protesting that on the basis of privacy.

    By Anonymous Anonymous, at 8:09 AM  

  • not very well, I'd imagine -- too many people face deportation.

    I think the best solution is per household, or maybe even per meter (if that's possible). You could avoid rich households gaming the system by requiring a substantial fee and/or justification to get a second meter.

    By Blogger Allison Kort, at 8:12 AM  

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