Rain and Smudgers

The Australians have been in the news again. This time it's about them fighting over toilet paper in the market aisles.

Which has got me to wondering how many liters of water we would need to flush toilets and keep the showers going.

For one, an average shower, unless you are a teen, lasts 8 minutes. An average shower spews out 8 litres/minute. That's 64 liters/shower. Of course, if you have teen girl, pre-employment, when time is immaterial, but fake-nature smelling soaps are, showers can be as long as 20 minutes, and if they had it their way, they would have a shower head that spews out 24 litres per minute. 280 liters/shower would be their norm.

The other favorite habitat of a teen girl appears to be the Bathtub.

Bath taps range from 10-16 l/m. Filling 2/3rd of a 180cm long bath (having a 275 liters volume), means 180 liters. So it can take 180/12 (=15) minutes to fill. And one can then spend an hour soaking listening to music from a cellphone. Sounds about right, from what I've seen.

Finally, it's worth knowing that the average tap in front of the makeup mirror delivers 6 l/m.

Of course, I could keep on thinking my way through the other rooms of the house, or skip all that and take LearnNZ'stats that – in New Zealand – the average person uses 227 liters of water per day:

  • Toilet = 86 liters per day
  • Bathing and hygiene = 68 liters per day. According to the above, they're not counting teens… (somewhere between 180 and 280, so 230).
  • Laundry = 36 liters per day
  • Kitchen = 32 liters per day
  • Housekeeping = 5 liters per day

That's interesting. 227, adding in the teen factor – which is admittedly only 1 out of 3 (2 parents, 1 teen) in this household, adds another 75 liters per person. Let's round it all to 300 liters.

Of course, there's also outdoors summer stuff - watering plants, filling wadding pools, etc. Add another 300 liters a day, but not every day. Let's say 150 liters a day.

450 liters per day, times 30 days a month = 13500 liters/month. 13500 liters/month, times (worse case scenario) 4 months of drought, equals = 54000 liters of water needed.

Which means 2 x 25,000 above ground liter containers should do the trick. 3 would more than enough (although that would mean 5 to 8 of the largest underground storage tanks…pretty expensive).

This aligns with advice that one should consider using at least 30,000 litres of storage, although if you also are planning on a lot of gardening, 3 x 25,000 would be more appropriate, as 4x30x650 is a lot of liters.

And how much roof is needed to fill that up again? Well, I found out that in Wellington it rains 247 days a year, dropping a total of 1243mm (sounds about right – for all it's self-hype Wellington truly is a wet blanket compared to the South of France…90 days, 550 mm).

1 mm of rain over 1 meter squared of surface = 1 liter.

So…1243/12 = 100 mm per meter / month = 100 liters / month is delivered via 1 meter squared of roof.

So I would need - to refill 55,000 liters of stored water - a minimum roof size of 550 sq.m if I wanted to refill in 1 month. Or over 2, 275 sq.m, over 3 months, 185 sq.m, and over 4 months only 140 sq.m.

That works. At least until global warming really kicks in. But it's worth knowing that the absolute minimum I should constrain designs to is 50,000 liters of water storage (preferably 75,000 liters) and a house size of no less than 140 sq.m of roof.

Fine. We've covered the basics. But let's get back to that issue of Australian ladies fighting over toilet paper for a second.

The following is a bit delicate – but it's important in the context of the Corona virus question.

When looking up the matter I came across a thread where they were discussing the the fact bidets are not common in NZ. I'm interested in this question because – especially in these times – using soap and water (and presumably singing Happy Birthday for 20 seconds..?) would be more hygienic than using “smudgers” (presumably because – as someone at some point in the thread so vividly described – sometimes “using toilet paper is like trying to wipe peanut butter out of a shag rug”.

I leave you with that thought. And am adding 10l/person/day to the above equations and adding bidets as a must in the house plan…


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