For those with Stainless steel sink and in the middle of renovation, sometimes the contractor uses the tap and the water came in contact with cement, tiles, clay, etc creating hard water and eventually leave with water marks and stain that is difficult to remove. I have scrubbed using towel but the stain still remain when the sink is dry. Here is how i eventually got it removed. Things used: Oxo Squeegee Heinz diluted white vinegarBicabornate of sodadry towel3M sponge Time required: 10 minutes it is actually quite easy to remove, all we need is some diluted white vinegar and bi-carbonate of soda. I tried the 'artificial' vinegar and it isn't as good as the Heinz one. Really powerful. I'm using a 3M sponge (green side) and a towel. bi-carbonate and vinegar to create a paste and use the 3M green side to scrub. Please do not scrub too hard, it will scratch your SS sink. Just lightly rub the stain off. Then use a dry towel to wipe off excess paste and see if the stain has been removed All done!