Hard water is full of calcium salts. This is why it can leave some really stubborn marks behind on your concrete surface.  The stains not only look unpleasant to the eye, but they can also make the concrete porous if not cleaned away. Luckily, removing hard water stains is not at all a big problem. Make sure that you have your protective gloves on before carrying out any of the procedure.

Use Trisodium Phosphate

If the stains are left on decorative concrete, then you should use trisodium phosphate or TSP, as it is most commonly known as. Simple take 5 gallons of warm water and combine 1 pound of TSP with it. Now rub the mixture on the stain with a mop or a rag. Wash it off with clean water and repeat as necessary.

Take Help of Hydrochloric Acid

Make a solution of 90% water and 10% hydrochloric acid. Before applying the solution on the stain, clean it with plain water. Take a coarse brush and clean the stain with the solution applied on it. Wait and let the solution fizz. Clean the area with water. Repeat if necessary.

Try Efflorescence Remover

If the stain resembles a chalk like residue then you should remove it with an efflorescence remover.  It is used on colored concrete and is very effective.