During a home inspection, something that comes up frequently in Cape Cod basements is the word efflorescence. What is it? I had to look up how to even spell it!
From a google search: “Efflorescence is actually a harmless crystallized mineral salt that has formed on your basement walls over time. … In cases where moisture bubbles up from your basement floor, it may even resemble a white “foam” on your floors. Efflorescence forms as moisture passes through the porous concrete of your basement walls.”
Now when your home inspector says…see that white line in the basement?…you will say ‘oh, the efflorescense?’ There you go! There are products to clean it or paint over it. As always, best to consult a professional.