Purification of water and air is a constant challenge to chemists and biologists.
One promising new line of research uses photocatalysis involving titanium dioxide.
Exposing TiO2 to UV radiation in an aqueous environment can lead to the formation of highly oxidising species derived from oxygen, which are capable of converting organic material (e.g. bacteria) to harmless inorganic by-products.
It has the added advantage that TiO2 is plentiful and cheap and uv light is readily and freely available from sunlight.
The version here uses a microscale approach to ensure that the reaction happens quickly.
(Many thanks to Kevin Jones of The University of St Andrews who devised the original experiment)
Photochemical catalysis – Risk assessment