Caller said he is Nick from Atlantic Water and Power offering water testing in exchange for a $25 gift card to Home Depot, Red Lobster, or Olive Garden. caller ID says Mary Smith
The usual scam is they want to come out to your home, do a free water test, prove you have bad water and hard-sell you on a water purification/filtration system costing $thousands. They may even offer a refund guarantee or some ridiculous warranty. People generally report great difficulty in getting a refund or exercising the warranty. You can buy equivalent systems for much less if you shop around.