Remove water stains from black slate?

I have the same problem and saw this on a different Q&A website. Am about to try it as it certainly seemed the best answer:

White vinegar is great for removing water stains from slate fireplaces, it has been tried and tested and proven to work. See the step-by-step method below...

Natural Formula to Use:

Pure white vinegar

Method to Use:

1.Fill a clean spray bottle with pure vinegar

2.Spray the vinegar freely over the fireplace and wait for a few minutes

3.If stains are stubborn spray more vinegar and wait a while longer

4.Simply wipe away with a clean cloth to reveal the shine

Sometimes stains are extra stubborn - for this make a paste of white vinegar and baking soda and scrub gently with a soft brush or sponge. Never use an abrasive cleaner like scouring pads, powders or steel wool as this will scratch the surface.