Rome’s famous Trevi fountain welcomes 10.5 million visitors a year. What is it about water spraying out of a decorative source that gets people hot and bothered? 

Lisa Aiken, the interior designer behind Terra Firma Design, chalks it up to the soothing sound and trance-like effect of watching moving water. In the early aughts, when she ran a garden store in Bloor West village, shoppers often stopped by simply to take in the aural pleasure.