The word waterlines 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: 15
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (73 words)
aeriest, antlers, antsier, arenite, earnest, eastern, elastin, elaters, entails, enteral, entries, eternal, lateens, latrine, leaners, leanest, lenites, lineate, nailers, nailset, nastier, nearest, newsier, ratline, realest, realise, realist, relates, relents, reliant, relines, renails, renewal, rentals, reslant, restain, retails, retains, retiles, retinal, retinas, retwine, salient, saltern, saltier, seriate, slatier, stainer, stealer, sterane, sterile, sternal, sweater, swelter, tawnier, tensile, tinware, trainee, trenail, triaene, trienes, twiners, wailers, waiters, wanters, wariest, wearies, weiners, western, wieners, winters, wrenlet, wrestle