OCEANSIDE -- Buy a plastic water bottle. Throw it away. Buy another.

That use-it-once mentality added an estimated 22 billion plastic bottles to the trash last year.

Entrepreneur Faith Paulus has an answer: a reusable sports bottle with an activated carbon filter that can be used 300 times. It's an appeal to the pocketbook as well as altruism: Save money and save the planet.

A designer by trade, Paulus researched how to make an environmentally appealing bottle and filter system, found a manufacturer, and in 2007 set up shop on South Nevada Street under the name Back to the Tap.

It's a small company. Manufacturing is contracted to a company in Texas, and Paulus is assisted by a handful of environmentally minded volunteers.

Paulus' venture has begun to be noticed. In February, she was chosen as a finalist for the Carlsbad Chamber of Commerce's Entrepreneur of the Year award.

"What a great place to do it, in Southern California, where everybody's outdoors doing sports," said Ted Owen, the chamber's president and CEO.

"When I used to ride my bike, I'd have two bottles of water. But you always run out, and end up throwing them away. But with this one, you don't have to do that.

The carbon filter appeals to people who don't like to drink tap water, or who may need to drink potentially unsafe water in emergency situations or overseas, Paulus said.

You don't even need to travel out of the country to find unsafe water, she said. As part of its charitable activities, the company has been providing bottles and filters to the community of Heber, near El Centro. The water supplies are contaminated and residents have been warned not to drink from the tap. The carbon filters make this water potable, Paulus said.

A company fact sheet says the filter removes protozoan parasites such as giardia and cryptosporidium, along with more than 99.99 percent of cysts and 99.9999 percent of bacteria, for up to 80 gallons of water.

The bottles are sold in two sizes: $17 for a 16-ounce bottle, and $22 for a 27-ounce bottle. They're made without bisphenol A (BPA), a chemical under study by the U.S. Food and Drug Administration because of concerns it may have some toxicity. However, the FDA has not issued any warnings about BPA.

The carbon filters sell for $25 for 2, which can be used in both bottle sizes.

Bottles and filters can be ordered online at www.backtothetap.com. The company donates $1 for every bottle sold to the programs of EarthShare, an environmental charity, Paulus said.

Combining environmentalism and entrepreneurism makes sense, she said, because people should be encouraged to take the initiative in tackling problems.

"We need to independently find our own ways of creating products and solutions, without necessarily waiting for government-based solutions," Paulus said.

Contact staff writer Bradley J. Fikes at (760) 739-6641 or bfikes@nctimes.com. Read his blogs at bizblogs.nctimes.com