The Denver Post, cited by Coyote Gulch, claims that low flow toilets are better now. My own experiences with these beasts, mandated by Congress, has been decidedly more negative. Simply put, they do a very poor job of sending feces down the drain, which is a mission critical purpose of a toilet. Pulling out a toilet brush, or hogging the bathroom while the toilet recharges for another dubious weak flush, are activities few of us relish.
True, I could have simply encountered old and inferior models. But, I am certainly not yet convinced and won't be until I have seen these allegedly superior new models myself.
Also, low flow toilets are a classic example of poor regulatory judgment. Toilet choice has a widespread personal impact on large numbers of people where even modest differences in quality are notable. The difference for a consumer between an old fashioned toilet and a low flow toilet is much greater than the difference between, for example, a car with a six cylinder engine and a four cylinder engine, that people are willing to pay a great deal of money to enjoy, despite significantly reduced fuel efficiency and increased pollution. Yet, no one is mandating four cyclinder engines for all sedans.
High flow toilets are not all that significant a cause of wasted water. In most arid watersheds, 90% or more of water is used for marginal, inefficiently irrigated horticulture, despite the fact that fishing and boating are more important to the local economy than the entire economic product of horticulture. Half of residential water use is for landscaping. A golf course uses as much water as roughly 800 homes. Slight increases in irrigation efficiency by the 1% of so of the population that uses irrigated horticulture (something that would also benefit the farmers themselves by reducing their consumption) and wider use of xeriscaping could produce far less intrusive water savings than the campaign for low flow toilets.
There are better places to seek efficiency in residential water use, even within homes. Simply fixing leaking in aging infrastructure can save a great deal of water. Even better would be to revamp water law and the regulatory structure to provide for wider use of gray water for appropriate purposes like toilet flushing. As I understand it, strictly speaking, gray water systems are illegal under Colorado water law. This doesn't matter for a few renegade do it yourselfers, but it means that systemic efforts to install or mandate graywater systems for new subdivisions and new construction are legally impossible. Gray water systems are far more water conserving (a 100% reduction in the demand for fresh water for use in toilets), while working better because they are the same toilets we used to know and love, with a different pipe hooked up to them.
Most water misuse is simply a product of economic incentives. Tap water is very, very cheap in the quantities used by a typical household. For farmers who irrigate, tap water costs just a fraction of that price. When something is cheap, it is used in excess. If we really want to promote efficiency with minimum inconvenience, we should increase the cost of water (perhaps with a tax, or a more efficient market in water rights), rather than take heavy handed steps that are far less efficient at conserving the resource.
Also, if we are to impose disparate prices, why not penalize less essential landscaping use rather than more essential in-home municipal use which is the smallest part of the water consumption pie. Denver Water already has a system in place to segregate the portion of each bill attributable to each kind of use which it uses to bill people for sanitary sewers, based upon baseline winter water useage. This would fairly reflect the fact that the last gallons of water Denver water buys, when it must increase its supply, are generally the most expensive.