In sci.skeptic Sylvia Else wrote:
[...]
A person may buy a rainwater tank because it makes them feel green (and
they like that feeling). If they do that, then that feeling is what
makes the value higher for them.
[...]

Turning to some facts we have surveys of why and how many Australians
have installed tanks upto approx 2008. According to some "no one" will
opt for a more expensive option, when there is cheap, desalinated water
around. The real world seems to have disobeyed the theory, again.

From the Aus Bur of Stats:

In 2007 (latest data available) 19.3% (1.5 mn) households have a
rainwater tank. Another 3.2% have a tank on order. This compares with
17.2% of hh in 2004 and 15.2% in 1994.

SA had the highest proportion 45.5% of hh; Qld is the 2nd highest at
22.1%.

Saving water was the main reason to install a tank (41.7%); 27.3%
installed a tank because they had no access to mains water; 19.5% were
concerned at the quality of mains water; 12% installed a tank to
reduce the cost of water; 6.3% wanted specifically to use the water
for outside use (e.g. during the past few years water restrictions
prevented or at least restricted using mains water for lawns, gardens
or car washing).

34% of hh 2007 reported they would not install a watertank because of cost.

--
R Kym Horsell

If your ideas are any good you'll have to ram them down people's throats.
-- Howard Aiken