The exact percentages don't matter as every home will be slightly different. What's important is the relative sizes of each.
Toilet
Did you know the toilet is the single largest use of water in your house? I sure didn't. But this means anything you can do to make your toilet more efficient will go a long way to saving water. I recently found and installed two products in my toilets that will greatly reduce the amount of water used.
1) New fill tower
The fill tower is what adds water to the tank after each flush, but it also adds water to the toilet bowl so the bowl has water waiting for your next "deposit." But the design of most fill towers wastes water, as much as half a gallon per flush. The part that fills the bowl, it can't shut off until the tank is full. But once the bowl is full the extra water flows over the trap and into the sewer. So with each flush you're wasting water and you don't even know it. This new fill tower has an adjustment that allows you to fill just the right amount of water for your specific toilet. And it only costs $10, a real deal.
2) Dual flush conversion
The say 4 our of 5 flushes is for liquids. Obviously "solids" need more water to flush down, but liquids could use much less. Wouldn't it be nice if you could tell the toilet a small flush or a large flush? Well with this product you can. This conversion kit has two buttons, one for liquids and one for solids. So you can select the right size flush and save tons of water. This kit only costs $35 and includes the above fill tower.
I believe in this product so much that I plan on writing a followup post to talk about this product, installation, etc.
Shower
After the toilet the shower is the next largest use of water in a typical home. Well over 95% of all shower heads sold in the US deliver 2.5 gallons of water per minute (the federally mandated maximum). A new low flow shower head will easily cut water usage. For example, a 1.5 GPM shower head will save a gallon of water per minute. So a 10 minute shower per day saves 10 gallons of water per day.
I think a lot of people are afraid of the words "low flow shower head." But they shouldn't be, the technology has gotten much better! I recently installed a High Sierra shower head (1.5 GPM) and it's a better shower than we got with out old 2.5 GPM shower head.
As with the toilet products, I'll do a follow up post and review of this shower head.
Laundry
Washing clothes is another large use of water in the home. But here's a place where it's not as easy to save water. Obviously you can do things like only was full loads. Beyond that the only way to save water is to buy a new high-efficiency front-load washing machine. Not everyone is willing or able to spend money on a new washing machine, which makes other simple changes like toilet products and low flow shower heads more important.
Faucet
The faucets in your house use about as much water as the shower and laundry. There are two simple ways to save water at the faucet. First, turn off the water when not in use. This sounds obvious, but it's not always so. If you're brushing your teeth, turn off the water while you brush. If you're washing dishes, turn off the water while you wash.
The second tip is to install new faucet aerators. These are inexpensive cartridges that screw into most faucets. Most likely your faucets currently have them, you can replace them with lower flow models. A standard aerator delivers 2.2 GPM, so if you install 1.5 GPM you'll save 3 quarts of water per minute. Aerators are cheap and easy to install. Best of all new aerators will probably perform better than your current ones because these get corroded and crusty over time.
Leaks
Leaks in a typical house account for significant water use. I'll cover detecting and fixing leaks in a separate post.
Dishwasher
The dishwasher is one of those appliances that people think use a lot of water, but in reality uses very little. In other words they are very efficient. A regular dishwasher uses only 6 gallons of water per wash cycle. A high-efficiency model uses about 4 gallons per wash cycle. So buying a new dishwasher is probably not cost effective to try and save water. But there are several tips that can help. First, only hand wash items that can't go in the dishwasher. Because the dishwasher is so efficient you'll most likely use more water (and soap) hand washing dish. Second, run the dishwasher when it's full, don't run partial loads if possible.
