Re: the water, sometimes it may depend on your building's age, and even the neighbourhood pipes (it has to come from somewhere, right?) I found those filters that attach to your faucet don't do very much except maybe some peace of mind; Boiling the water is just common practice for us, and by itself won't actually remove any micro particles and such. We ended up getting an RO filter installed under the counter (check on the web "Reverse Osmosis"). Of course it also depends if you are renting your flat, how much you would like to invest since it's not something you would easily leave behind if you moved.
For the air quality, an air purifier has helped us. Make sure your a/c units are clean and you may consider some of the newer technologies like Sharp's "plasmacluster" and Panasonic, etc. have similar products out. Check out this link, though it may be slightly outdated: http://www.cleartheair.org.hk/aircleaners.htm