Great Idea! There are several ways to reduce your carbon footprint, save water, and also save some money on utility bills.
LED light bulbs: Switching to LED light bulbs is the lowest hanging fruit for all. Replace your traditional incandescent or CFL bulbs with LED bulbs. These have a longer lifespan and consume far less energy to provide similar luminosity.
Seal air leaks: Air leaks around older wooden windows, doors, and other openings can cost you a ton! Seal them with Silicon, Caulk or Weatherstrips. Better yet, replace them with UPVC / Aluminium doors & windows when you get a chance.
Programmable thermostats: For those living in areas with extended hot summers, air-conditioners can be adjusted to shift to higher temperatures at certain hours when you are not likely to get up and do it yourself, for example middle of the night.
You could also move to energy efficient appliances and use reflective tiles & paint on exterior of your house / office building.
As for water conservation – you can install low-flow showerheads and faucets, use WCs that consume less water while flushing the toilet, and recycle the water discarded by R.O units in your kitchen.