Landscape water use (at least in the dry west) is often the biggest single water use, often resulting in a doubling (or greater) of a home's average water use, but in most cases on a yearly basis indoor water use is more significant. Of the two, indoor water use is somewhat easier to reduce since usage is more dependent on personal choice. Landscape water often has a bigger impact on water supplies, since the periods of maximum need corresponds to periods of drought, when water supplies are the most challenged. Those who want to keep their landscapes alive (and maybe looking good) during drought should consider a gray-water system or a rainwater tank.
Whether you're on a well or city water, in most cases saving water saves energy too, because it takes energy to pump water and treat it also.
Indoor Water Conservation
Tops on most lists are toilets, although now that 1.6gal/flush toilets are the standard, all new toilets are quite good. Most of the performance problems with early 1.6gal flush toilets have been fixed, although to be sure check www.savingwater.org for a performance report on which toilets flushed the best. Newer, "ultra low flush" toilets use around 1.28gal/flush are even stingier on water(look for the "watersense" label, see the EPA's watersense site), and dual-flush toilets have a half flush option of around .8 gal/flush. The people living in arid areas, the rule "if its yellow, let it mellow" saves even more water by avoiding some flushes altogether, but does result in having to clean the bowl more often.
Low water use washers and dishwashers will also save a lot of water, the best models use less than 1/2 the water of older models. For a complete list see, www.energystar.gov for listings.
Low flow faucets only save water for those who turn them on full blast, although they do aerate the water better, resulting in better wetting with less water. For low flow showerheads, the improved wetting is the main advantage for the water conscious, while the lower flow is an annoyance to some, claiming that it makes their shower take longer.
Using PEX home-run plumbing for hot water delivers hot water faster, and saves both energy and water. Locating the hot water tank close to the fixtures is equally effective.
Fixing leaks of course, whether in faucets or toilets is a big water saver. Even the slowest leak can easily add up to ten gallons a day.
Reducing water use in landscaping is a matter of three things: good soil, choosing plants that belong in your climates and placing them in the right microclimate on the site, and selecting among those plants, the more drought tolerant ones.
Site protection: Although there is much to know about protecting a site during construction, that is mostly beyond the scope of this document. There are a few simple ideas to look for. Preserve whatever topsoil is already there. Desirable mature plants, especially trees take many years to replace, so it pays to treat them well. In particular avoid disturbing their roots via digging or driving machinery over them. Don't let your soil get washed away during construction, even if its lousy soil, because if you don't want it neither does your neighbor, nearby stream or sewer system.
Unfortunately, the common practice in development is to remove most of the topsoil, leaving a very poor soil behind. Bringing loads of compost (up to one foot deep of it) will bring those soils back to health. Make sure you till up the mineral layer and mix it with the compost as well as you can.
Eco-friendly landscaping: Traditional American landscaping consisting mostly of turf grass is often a significant source of pollution (fertilizers, herbicides & gas mower exhaust) as well as significant use of water during the summer months. The environmentally friendly landscaping eliminates most or all of the turf grass and produces little or no pollution while also requiring much less summer water. The components of an environmentally friendly landscape include:
Good soil, or more specifically soil that your chosen plants want to grow in
Plants suitable for your climate and placed in the correct place in your yard
Needless to say doing this is not without it's drawbacks, specifically that it is no longer possible to maintain your yard by machine, and if you're looking for a place to play croquet, you have to go elsewhere. On the other hand, few other plants require as much maintenance as turf grass. Garden lovers tend to have a wide variety of plants that create interest throughout the growing season, but this isn't necessary to create a more environmentally friendly landscape since you can use limited number of very tough plants and just trim them when necessary. Weeding is necessary until your garden plants squeeze them out, so the first couple years are more work than subsequent years. Unlike turf grass, you can't use weed killer on them, because it will kill many plants also. If you're planning on maintaining your own yard (as opposed to using a lawn service), a yard with no turf grass is no more work.
Landscapes tend to use a lot of water if you want them to look good, whether they are turf grass or perennials. If you want to use less water, drought tolerant perennials can give you a more interesting landscape without using any water after the first two years.
Soils are a combination of organic material (compost, humus), and mineral soils: sand, clay, and silt.1
Water - Extending Your Supply
Traditionally the most common uses of rainwater and graywater are in areas with no public water and limited well water, but due to higher water rates and overtaxed water supplies, even people on city water are looking other ways to supply their water needs (mostly landscape water).
The common solution to this has been to build a cistern which is then used for yard water, and possibly flushing toilets and maybe washing clothes. City dwellers on small lots will generally be limited to either small above ground tanks or putting their tank below ground somehow. While above ground storage is typically cheaper than below ground (if for no other reason than you avoid having to dig a very big hole), it can occupy a lot of space and the top of the tank must be low enough that water from the roof will flow down into it. Typical tanks are plastic, fiberglass, metal and concrete, although there are other materials that can be used also.
A complete water system is a non-trivial thing, and it will typically require some yearly maintenance to clean and/or replace filters. In addition to a tank, a complete system includes one or more filters to keep debris out of the tank, another filter in the tank to protect the pump from debris that does get in, a pump and its pressure regulation equipment, and finally a filter to remove dissolved sediment. If the rainwater is to be used for drinking, much more sophisticated filtering is needed to remove any chemical, bacteria and viruses as well.
In almost all case the urban dweller will not be able to rely on their cistern to supply 100% of their needs (unless they have room to build a very large cistern!), so some method of reverting to using city water will be necessary.
The cost of rainwater systems is not cheap. Tanks range in typical price anywhere from fifty cents a gallon to more than a dollar a gallon, while the rest of the system can easily cost a couple of thousand dollars. A person with knowledge undoubtedly can do it for much less. One of the biggest limitation for the city dweller is the lack of people skilled in designing and installing rainwater systems.
Rainwater - TBD
Seattle DPD Green Home Remodel Guide - Bath and Laundry here.
Seattle DPD Green Home Remodel Guide - Landscaping here.
savingwater.org toilet test info for efficient toilets
http://www.epa.gov/watersense the EPA watersense website
1: in very arid climates, there is little to no organic material and so that's what those plants will thrive in. In other climates, certain plants prefer little to no organic material, so you can leave an area with no organic material if you choose those plants.