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Thanks for your replies. There doesn't seem much enthusiasm for filtered water, apart from avoiding fur in the kettle. For just one or two cups of tea, boiling a measured amout of tap water in the microwave is quicker than boiling a kettle. Whether it uses less electricity is another matter. "The Water Supply (Water Quality) Regulations 2001" on the internet may be of interest. I've come to the conclusion that filters are not necessary, especially at the price and will probably not buy any more.