The word headwaters is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 16
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (44 words)
adheres, aerated, aerates, ashweed, awardee, dearest, dearths, dewater, earthed, hardest, hatreds, headers, headset, hearsed, hearted, heaters, hetaera, reasted, redates, reheats, resawed, rethaws, seaward, sedater, sheared, steward, strawed, strewed, swathed, sweated, sweater, tarweed, tasered, teaware, threads, trashed, warhead, watered, weather, whereas, whereat, wreathe, wreaths, wrested