Not that long ago, reusable bottles made of clear, hard, polycarbonate plastic were the hippest water carriers to have, beloved by hikers and college students alike.

Then came a draft report from the National Toxicology Program in April 2008 about possible health risks from a chemical in the polycarbonate known as bisphenol A (BPA). Though it soft-pedaled the reasons for concern (there is actually an alarming amount of scientific evidence that BPA may be highly toxic), the news was widely carried in the media and the bottles' appeal evaporated overnight.

In response, Nalgene, the manufacturer whose name had become synonymous with this type of bottle, announced it would phase out the product and replace it with a new model that was equally clear, hard, beautiful -- and BPA-free.

So -- problem solved.

Or was it?

The new Nalgene water bottle is made of a "copolyester" plastic manufactured by the Eastman company with the trade name Tritan. So are new bottles by Kor and Camelbak. All trumpet the fact that their bottles are BPA-free, with the implication that BPA-free is the equivalent of safe. But we have no way of knowing because the ingredients that make up Tritan have been kept secret. They could include another dangerous chemical...or not. Since the ingredients have not been identified, no one can say.

All we know about the Tritan bottles is that, like polycarbonate, they fall into the #7 category of "other" plastics in the identification system used to mark plastic containers. (The numbers appear inside a triangle of chasing arrows.) When it comes to 1 through 6, the numbers are relatively informative, but 7 is the mystery number. Here's the lowdown on each:

• #1 (PET or PETE) plastic is the kind used for bottled water bottles, which are generally regarded as safe. They have been shown to leach antimony into the water in a couple of studies, but at levels considered safe by the EPA. The scare about their leaching DEHA if reused, which you may have come across, turns out to be an urban legend. If there is any risk from reuse, it probably comes from bacterial contamination. (The bottles' narrow necks make them hard to clean.)
  
  
• #2 (HDPE), 4 (LDPE) and 5 (polypropylene) plastics are generally regarded as safe.
  
  
• #3 (PVC) and 6 (styrene) plastics pose health risks and should be avoided. (They are not ordinarily used for water bottles, but are used for other food and beverage containers.)
  
  
• #7 plastic is usually polycarbonate and contains BPA. If you are in love with a particular #7 bottle, you could call the manufacturer to identify the plastic, but that might not make matters clearer. Learning, for instance, that the plastic is Tritan would not tell you enough. The "better safe than sorry" approach would be to avoid #7 altogether in my opinion.

Despite the "generally regarded safe" remarks above, a recent analysis by the Milwaukee Journal Sentinel of 10 products advertised as microwave-safe found that BPA leached into food from packaging labeled #1, 2 and 5. This analysis was part of ongoing coverage by the paper of chemicals in consumer products in a series called "Chemical Fallout," which won the 2008 John B. Oakes Award for Distinguished Environmental Journalism.

If this leads you to feel queasy about plastic in general (I still use it, though never in the microwave), consider food-grade stainless steel for your water bottles. Klean Kanteen and New Wave Enviro are two companies that offer such products. Both provide a choice of caps made of stainless steel or plastic.

Some people object to the fact that these stainless steel bottles are manufactured in China because of the lethal contamination recently found in several products made there. If that concerns you, I suggest you call the bottle-makers (both American) and ask what steps they take to ensure their bottles are safe.

As to the popular aluminum bottles made by Sigg, they have a lining whose ingredients, like Tritan's, have not been disclosed. Sigg does state categorically that tests show the lining does not leach BPA, and there is no reason to assume otherwise. But this is another case where a manufacturer could assuage doubts by being more forthcoming.

I wish I could tell you about the newer corn-based plastic bottles, but I haven't been able to find enough information about them.

If none of these choices strike you as perfect -- well, it's not a perfect world. However, better health and safety regulations would help, starting with labeling requirements that tell the public what food and beverage containers are made of.

ONLINE RESOURCES SWITCHBOARD Bisphenol A: Is it Gone? What's Next? NRDC Chemicals in Plastic Bottles JOURNAL SENTINEL Chemical Fallout Watchdog Report FAST COMPANY The Real Story Behind Bisphenol A THINK FORWARD Why the FDA's Notion of BPA "Safety" May Not Pass the Laugh Test LIFEWITHOUTPLASTIC.COM Non-plastic Products

Be careful with sippy cups and baby bottles. Babies and young children are at greatest risk from BPA and other toxic chemicals because their systems are developing and more prone to damage. Protect them by avoiding polycarbonate cups and bottles -- and not heating their beverages (or food) in any kind of plastic. If you own a clear, hard plastic cup or bottle and don't know what it's made of, assume polycarbonate and use something else.

Sippy cups and child-sized cups and mugs are available in stainless steel and safer plastics. Baby bottles are available in glass. If your baby is on the way, remember the breast is best for a host of reasons -- but be careful about the products you use personally. Besides polycarbonate water bottles, avoid or cut down on canned foods. The lining in cans is also made with BPA.

Pack a safe lunch. In place of soft plastic lunchboxes made with PVC (one of the toxic plastics), try organic cotton lunch sacks or stainless steel lunchboxes. For beverages, use canteens or bottles made of stainless steel or one of the safer plastics; for food, stainless steel containers. If your children are old enough, you could use all-in-one, stainless steel tiffin boxes and do away with lunchboxes completely.

Check your water jug. Those giant jugs of bottled water delivered to homes and offices are often made of polycarbonate. You can look for the telltale #7 on the plastic, but remember it's not conclusive. Call the company to find out for sure what the plastic is made of.