Large shiny water tanks litter the roofs of Chinese "suburbia". These great little devices are a side offect of the small size of a residence, which often leaves as much as possible outside the windows or doors or even on the roof, and also a great way of boosting efficiency and keeping bills down. It's hard to buy non-energy saving bulbs, and public transport is always packed, as are the cycle lanes. This may be a polluted country, but the people are often much less damaging to their immediate environments than their western counterparts.
The large square connecting the tank to the roof is full of small, thin pipes. These help circulate heat and cover a large surface area, ensuring that water is warmed by the sun.