Evian, Perrier, Poland Spring — bottled water has become ubiquitous in the U.S., and the resultant plastic containers are posing an increasingly serious problem by clogging landfills and contributing to air pollution. In California, where bottled water is particularly popular, the state Department of Conservation is unveiling a campaign this week to convince consumers to recycle rather than throw away their empties, and two state legislators are sponsoring a bill to double the refund on water bottles. To date, only 16 percent of plastic water bottles are recycled in the Golden State, despite the current cash refund of 2.5 cents for small bottles and 5 cents for larger ones. The unrecycled bottles — some 3 million of them every day — enter the waste stream, where they take up space in landfills or are incinerated, yielding toxic fumes. If recycled, that quantity of bottles could be used to make 74 million square feet of carpet or 16 million sweaters.