Whether you're growing food or flowers, that garden requires watering if you want it to stay alive. Trust me. I have killed more than my fair share of plants by just plain forgetting to water them. Outdoor water use, such as watering your garden, is a major factor in a home's overall water usage, and it's also an easy one to fix with a rain barrel or two and a garden irrigation system.
A rain barrel is just what it says it is – a big barrel for collecting rainwater, often with a spigot at the bottom. You can purchase rain barrels at a hardware store or make your own. If you're planning to use your rain barrel to water your garden, I recommend putting it up on concrete blocks. The extra height uses gravity to give your hose some extra water pressure.
To make your rain barrel even more efficient, it's a good idea to set it up under your gutter's downspout. This way, rain water gets funneled off of the roof and right into your barrel. This isn't terribly difficult to do yourself. Just set the barrel up on a corner of your house, measure how tall it is, then saw off the gutter so that you can fit the barrel underneath it.