South Australia takes the cake and has the dubious honour of being the driest place in Australia. Spare a thought for the people of Adelaide they are running exceedingly low on the most precious commodity. I digress, Perth being the second driest capital in Australia gets much of its water from also quite limited subteranian aquafers. In many areas of the costal plain on which Perth is situated the water in these aquafers is highly highly mineralized mostly with iron. As a consequence where vegitation is irrigated the over spray falls on fences, walls and pavements, as a result these surfaces over a period of time become stained by the water. Sometimes it just looks just plain grubby but often it compliments the colour of the surface it falls on and forms subtle gradients of colour.