There are so many good toilet choices available:
Toilets are rated based on their gallon per flush (gpf). Low-flow toilets, using 1.6gpf or less , are now the federal standard. High-efficiency toilets use 1.3gpf, and others use as little as 1.1gpf. Dual-flush toilets have two gpf ratings, solids are flushed at the higher 1.6gpf rate, while liquids use 1.1gpf or less.

Changing out those old water guzzling toilets would be a GIANT step towards Going Green! 

Other eco-friendly choices you could make

A Bright Idea
Going Green is as easy as screwing in a CFL lightbulb. Go Green!

Water Smart
A simple hardware store item called an aerator on your kitchen
and bath faucets cuts down on water consumption, sacrificing
very little, if any, water pressure. For less than $15.00 you can
install one yourself and save up to 500 gallons per year. Go Green!

Think Small
The kitchen is the energy use capital of the home. If you are
planning a remodel, building new, or just replacing old appliances,
remember bigger isn't always better. In addition to looking for
energy-efficient ratings consider going for a smaller model that will
naturally use less energy. Best new appliance: The drawer-style
dishwasher. It allows you to do a small load of dishes without
feeling guilty! Priceless! Go Guilt-free Green!

Shower Power
Remember when the low-flow showerheads first came out? Instead
of the usual 10 minute shower, it took you 20 minutes just to get
the soap out of your hair! Counter productive wasn't it?
Well...those showerheads have come a long way since then, managing
to keep the water pressure and limit the flow. Love it. Go Green!

Heating Things Up
If your water heater is the 7 to10 year old range (that's 70 in water heater
years!) consider installing a tankless water heater. Here's the thing, a
tankless water heater only heats the water when hot water is needed, genius!
A tank water heater continually heats the water, whether you
use it or not, resulting in continuous energy use. Go Green!