To make her drama about the ritual shunning of widows in India (it's set against Gandhi's rise in the '30s), director Deepa Mehta had to endure the destruction of her sets by Hindu protesters, who burned the filmmaker in effigy. Completing this movie was a heroic act, yet Water, the final chapter in Mehta's feminist trilogy (Fire, Earth), is, alas, the weakest. Banished to an ashram, the widows are treated like spiritual lepers, but the movie takes the form of a lackluster women's-prison picture. Will Kalyani (Lisa Ray), who attracts a wealthy suitor (John Abraham), escape her fate? The question would matter more if the two didn't come off as moonlighting Vogue models, or if Chuyia (Sarala), an 8-year-old ''widow,'' were less puppyishly perky.