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Saturday, 19 April 2008

Stats Update - now including tank water

Here are the latest stats for our electricity and town water consumption over the past 25 days, plus some new information on our tank water use.

Electricity consumption has increased again.
This period: 8kWh per day, or 333W continuous
Previous 21 days: 6.84 and 285
Average since start of year: 7.62 and 317.

Town water use is also up. I think it's largely my fault... love the hot showers in cooler weather. 189L/day vs 130 in the previous 21 days and 164 average since the start of the year.

I may have mentioned when I was planning my tank installation that I considered getting a water meter to measure how much water we pumped from the tanks. Well I didn't do that, but I did fit a water level gauge which shows the height of the water in increments of 10cm. I also bought a rain gauge at the start of February and started keeping records of daily rainfall, and I noted on which date my tank was last filled completely. I've observed that 1mm of rainfall causes a rise of 20mm in the tanks and I've calculated that 100mm of water in the tanks is very close to 800L.

Armed with all this information and the current gauge reading, I can estimate how much water we've used and when it's likely to run out. In the 21 days since last full the tank level has dropped from 110cm (full) to 70cm. Rainfall of 11mm has added about 22cm to the tanks, so we have extracted about 62cm in total. That works out to about 4960L, or 236L/day. At that rate we have enough water to last another 24 days without further rain and a full tank would give us 37 days supply in a dry spell.

What's startling here is the overall amount of water we're using... 189+236=425L/day. It's quite a bit more than before we had the pump installed but we aren't using any significant amount of water outside. That means we're using more inside.

The laundry has to be the main culprit. Once we had the washing machine hooked up to the tanks we started using cloth nappies for our infant instead of the evil but water-efficient disposables. So every day or two we now go through a big bucket of tank water for soaking and then an extra load of washing. Combine this with my slackening frugality in the shower and you would probably account for most of the roughly 100L/day increase compared with figures from six months ago.

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