Do you drink tap water? There's mercury in that. It's in electrical appliances like tvs, computers etc but they're slowly phasing it out. Mercury is in energy saving light bulbs and some sick people get worse using them. I got rid of all mine and went back to the old style bulbs.
I got a Berkfeld water filter that's less than £100 and mine holds around 7 litres or a days supply of water. I highly recommend them because where reverse osmosis units remove the beneficial minerals and nutrients from the water and are expensive because most of the water is wasted the Berkfeld retains nutrients, eliminates almost all metals and other nasites and you don't waste a drop of water. And they're cheaper! I wouldn't do without it now but it's ok because it should last a life time.