Limits to Growth: The Water Supply

I've been looking though the old States Minutes from 1985, and some quite interesting figures emerge.

The yield per annum of the main water supply, factoring both Queen's Valley and the Desalination plant is:

Val de La Mare etc 929,000,000 gallons per annum
Desalination 300,000,000.00 gallons per annum
Queen's Valley 475,000,000.00

Total 1,704,000,000 gallons per annum

Now back in 1985, when they were making assumptions for the year 2000 - which is why they argued for flooding Queen's Valley - the considered the following:

a) A maximum demand per head of 40 gallons per day, which is also supported by current supply figures.
b) No expansion in tourism demand - the industry has in fact been able to maintain its demand for treated water at a more or less constant figure by restraining use and investing in borehole facilities in a number of places.
c) Industrial demand increasing by 10 per cent - this trend is confirmed.
d) 0 per cent saved by metering. The States subsequently decided against domestic metering.
e) Unaccounted for use limited to 16 per cent.

For a population of 90,000, this means a demand of 40 x 90,000 x 365 = 1,314,000,000 gallons per annum

Even allowing for the cancelling out of some of b) to e), this means we are below the total of 1,704,000,000.00

But - just accounting for the population - ignoring all the other uses, this means that when the population reaches 116,712, we will have run out of capacity. In fact, because of other demands this may well happen before this limit.

It also does not take into account how soon the reservoirs will take to run dry in a drought. But it does give us a maximum figure beyond which the population cannot easily expand.

Now if you take out the Desalination plant, it reduces to a maximum of 96,164 before the population consumption per annum exceeds that of the reservoirs. Not far off the present!

I'm sure there must be similar limiting factors with (1) sewage treatment (2) electricity capacity.

Even despite the French link, only so much power can be pulled over from France. And as far as sewage treatment goes, there must be a limit on the speed at which the existing system can cope with sewage, and the amount generated per head of the population. If anyone has any figures, I'd be pleased to work on them. This kind of calculation is rough and ready, but it certainly can provide a warning note which we would do well not to ignore.