On the backsplash around the counter in my master bathroom, there is a white powder that has formed on the grout between the tiles. It appears to only form on the grout. It has formed several times over the last few years and my wife usually just brushes or washes it off. The tile is behind the sinks in the counter but the grout and tiles do not get wet. I have the same tile and grout in the master shower and no white powder forms there where the grout is subjected to a lot of moisture.
Any ideas as to what this white powder may be and how to prevent it from forming? I have heard that sealing the grout may help. I have no idea whether the grout was sealed when it was installed. Is that a solution or is there something else?