I haven't... 30 gallons per day?
I thought the North American Wasteful Standard was 100 gallons per
day, and I know the regional water authority just asked our town to
get us down to 65 gallons per day. Several people in the newsgroup
seem to live on a lot less, though they may move some of their water
use elsewhere. 8*)
You can read your water bill (or meter) and divide by the number of
people in your household to see what you are currently doing, or pick
a number in the 50-100GPD range.
Having read of the 10'x16' Manhatten "condo"
that recently sold for $135K (plus a $505/month maintenance fee), I've been
thinking it would be nice to build self-sufficient, solar-heated, water-
ballasted greenhouse structures on flat city roofs...
Because roof space is free? Cost of water is hardly going to be your
only utility...
(this is 200 cu. Ft. (6x6x6 ft.) and weighs 5.6 tons + weight of tank)
You better talk to your building engineer...
I didn't quite follow the algorithm you suggested, although I can imagine
something like "Start with no cistern volume. Add rainfall. Consume water.
If we are out of water, increase the cistern volume until, figuring backwards,
we wouldn't have run out of water."
Close, it's more like "Start with zero volume. Every day add rainfall
and subtract GallonsPerPersonPerDay. Discard any overflow above zero
and record the largest _negative_ number you see." Similar to having
a cistern that's too big and recording the level you use it down to...
Seems to me this would overestimate the
required volume if the data record began with a few dry days.
Yes, but either you assume some starting amount of water (maybe you
are going to fill your cistern with city water the first month?), or
you are going to end up in a similar situation to the real world,
where you build your house and start occupying it at some time which
may begin with a few dry days.
How do we determine the catchment area and the economic balance
between the collection and storage costs?
For catchment area take the long-term average daily rainfall and
GallonsPerPersonPerDay and calculate how many square feet of roof you
need to collect that much water. That's PersonUnitRoof in the code,
the amount of roof collection area one person needs (long-term).
Balance between collection and storage costs is an interesting
question, I suppose you'd have to iterate over the dataset several
times with PersonUnitRoof increasing from it's minimum value, but I
can't imagine letting your water cistern size effecting your house
size. IMHO it's always cheaper to build more cistern than more
house...