A few weeks ago, I was watching a TV programme called This Old House, which showed workmen doing up an 1883 house in Manchester, Massachusetts. The Manchester project has been This Old House's biggest project to date spanning 22 months and a $1.5 million (€1.66 million) investment.

One of the side trips during the programme was to the Kohler Company showroom in Wisconsin. Kohler designs products for the kitchen and bathroom, and is one of the largest and oldest privately held companies in the United States.

Kohler employs people with doctoral degrees in multiple-test laboratories who spend their days figuring out what toilets do on a computer screen.

"It literally is rocket science compared to 20 years ago," said Mr Michael Chandler, marketing manager of Kohler's sanitary products. "Now we look at computational fluid dynamics. We predict every single surface and we design the inside of the toilet trapway on computers. We have developed toilet technology in a way that no-one else can do."

The company has used computer-aided engineering to design a toilet engine that meets the challenge of using only 1.6 gallons of water per flush.

Unlike Europe, which has used 6 litres (or 1.6 gallons) for decades, a federal law enacted in the United States in 1992 stated that any toilets sold after January 1, 1994 could use no more than 1.6 gallons of water per flush instead of the previous 3.5-gallon-per-flush counterparts.

"The general observation is that flushing technology in Europe is different," Mr Chandler said. In the Republic, for example, households generally use "wash-down" toilets, which means there is less water inside the bowl and the volume is low.

"There is a pretty high incidence of odour and people need to use fixtures to remove residue," Mr Chandler said. "Culturally in the US, this is not accepted."

As a result, Kohler has spent the past eight years designing and perfecting a flushing system called Ingenium that contains 0.6 gallons of water in the bowl and one gallon in the tank. It is a gravity-fed, siphon-jet system with all internal components designed to operate concurrently.

By using only 1.6 gallons of water per flush, the Ingenium flushing system conserves up to 11,000 gallons of water per year for a family of four. This water saving not only makes it environmentally friendly, it also lowers water and sewerage bills, and can extend the life of a well or septic system.

The Ingenium water surface - among the largest in the industry - provides for better hygiene as it helps maintain a cleaner bowl. It also prevents residue from accumulating, meaning the toilet requires less-frequent cleaning. The large water surface also reduces odour and aids the flushing action.

After so many years perfecting the toilet, Mr Chandler is confident that the 1.6 gallon toilet is comparable to its 3.5 gallon counterpart. "People don't have to worry about performance anymore," he said. The same technology is also moving over to the kitchen faucet and bath groups.

A report written four years ago by Potomac Resources in Washington DC called Saving Water, Saving Dollars looked at the efficiency of plumbing products.

When consumers in San Diego were asked how the 1.6-gallon-per-flush toilets work, 43 per cent said better than the old toilets and 50 per cent said as well as the old toilets, with 5 per cent saying not as well and 2 per cent giving no response.

When asked if, given the chance again, they would replace their old toilet with a 1.6-gallon-per-flush unit, more than 80 per cent said they were very likely or somewhat likely to do so.

In New York city, which operates the largest municipal water supply system in the country, there are 7.4 million residents, along with commercial and industrial water users.

After nearly three decades of steady growth in water consumption, three drought episodes occurred during the 1980s that resulted in water-use restrictions.

Action by the New York City Council established the 1.6 gallon per flush as the standard for all new toilets installed in the city as of January 1st, 1992. In 1994, the city introduced the Toilet Rebate Program to encourage rapid replacement of inefficient fixtures. Rebates of up to $240 were offered for the first toilet replaced in residences. Rebates for commercial locations were $150. Showerheads were also replaced at the same time.

Between March 1994 and April 1997, 1.3 million inefficient toilets were replaced with 1.6-gallons-per-flush units. The city paid out $290 million in customer rebates.

The Department of Environmental Protection estimates citywide savings to be 70 to 80 million gallons per day, and in a survey of 67 participating apartment buildings, the department found an average reduction of 29 per cent in water use.

Although the city's population is growing, per capita water use in New York has dropped from 195 gallons per day in 1991 to 164 gallons per day in 1997. The benefits of lower water usage will be seen again this year with another drought emergency in effect.

"In the past, we used to design everything by hand - we made millions of pieces," Mr Chandler said. "Today, through the use of computers, we can design and predict what toilets will do before we make them. I know the ones we make today get the job done."

He said people are no longer asking for toilets that flush well but for higher height toilets, comfort height toilets and heated toilet seats. They are choosing different shapes, colours and surfaces like vitreous china, stainless steel, glass, fire-clay and cast iron. "Trend-wise we're not just designing toilets on the computer but we're developing new creature comforts," he added.