Bathroom fittings maker Methven has fallen foul of the competition watchdog for allegedly claiming its flagship Satinjet shower heads save more water than they do.The Commerce Commission confirmed yesterday that it intends to prosecute the publicly listed company for misleading advertising under the Fair Trading Act.Methven believes the complaint was initiated by a competitor.The problem is the extent to which the Satinjet shower heads can save water and energy.Methven says its claims - that a Satinjet head uses up to 55 per cent less water and 45 per cent less energy - are true if the household is connected to mains pressure that delivers a flow of 20 litres per minute.The Energy Efficiency and Conservation Authority says the average water flow rate in New Zealand homes is 10 litres per minute.Around two-thirds of households have a water flow rate of 6-12 litres per minute, 14 per cent have 12-18 litres per minute, and just 7 per cent of the New Zealand population have a water flow rate of over 18 litres per minute.Methven New Zealand chief executive Gary Nel said the company was surprised the Commerce Commission had taken things this far. Once the watchdog had brought the matter to its attention it had changed the wording of its advertising and made it clear the savings related to high pressure water flows."I guess we could have been a little bit smarter with our wording but we didn't really think it was that much of a problem."In a household with a water flow of 14 litres per minute a Satinjet shower head could save 30 per cent on water and 24 per cent on energy, he said.The Satinjet shower heads, launched in 2004, have been a big hit for the company. In Australia, where water conservation is a significant issue, sales of the product rose 17 per cent in the last financial year. Nel said its advertising hadn't been an issue in Australia where most homes had high pressure water.He said the company stood by its product."Of course it's a concern and we're disappointed with [the commission's] decision."The Ministry for the Environment's sustainability.govt.nz website says the average shower head with mains pressure delivers at least 12 litres of water a minute.Low flow shower heads have flow restrictors built into the shower head and reduce the flow to about 5-7 litres a minute.The former Labour Government caused a furore last year by suggesting showers should be limited to a six-litre-a-minute flow.Methven shares closed down 5c to $1.30 yesterday.