So you're out on the trails, running or hiking, and it's a hot day, and you check your water supply (you did remember to bring water with you) and you realize that you've run out of water and forgotten your filter. Then you look at the gorgeous Alaska stream next to you and think, hey, there's plenty of water around here. Think twice. Depending on where you are, that great looking glacier fed cold Alaska stream could be overwhelmed with the carcasses of rotting salmon (where do you think they go after they spawn?) or it could be teeming with a microscopic parasite or two, which if ingested, could ruin your whole trip and cost you big bucks. I'm worried about the intestinal parasite, Giardia intestinalis (sometimes referred to as Giardia lamblia). See those white things trailing off the end? Those are flagellae, which help it move. Giardia is passed through fecal to oral route--basically the animal or person defecates the cysts and those get into a new host, either through the water (the cysts can live for up to a month) or by hand--as in changing a diaper. Ned Rozell, a science writer in Fairbanks, always treated his water in the wilderness--he thinks he got Giardia by ingesting a small amount of contaminated water.

The truth of the matter is that Giardia is not found only in Alaska--you can ingest these cysts pretty much all over the world. It's just that when people come to Alaska, they want to believe that the streams are pure.

What are the symptoms? It depends on you. Some people get raging diarrhea with the onset of symptoms occurring about 7-10 after ingestion. Other people have more mild symptoms: bloating, gas.

Can you diagnose and treat yourself? Well, if you were out in the wilderness, drank the water (I can lead you to a filter, but I can't make you think) and came back into civilization with diarrhea that would not go away, Giardia would be top on the list of what your doctor thought you had.

Here's the clincher. Consider the cost of going to see the doctor (good luck with getting an appointment around here in the summer--all the docs in town are out flying their planes and fishing): 1) office visit: $200; 2) stool parasite check (you get to provide the sample) at least $200--sometimes the lab needs more than one specimen; 3) antibiotics $20 (I think there's a cheap antibiotic for this--but not everyone can take it); 4) time lost from your vacation: priceless.

You know me. I'm all about prevention. So what are your choices?

1. UV pen--considered a water purifier--uses ultraviolet (UV-C) light rays to sterilize clear water by destroying protozoa (including Giardia and Cryptosporidium), bacteria and even viruses. Cons: uses lithium batteries, not thought to work as well with murky water (the UV rays can't transmit as well)
2. Water filters--these physically remove particles, protozoa, and bacteria--look for one that goes down to 0.2 microns in size--there are also some new high flow filters available. One of the problems in the past was how long it took for the filters to work.
3. Chemicals--"water purification"--the two main choices are iodine and chlorine. Iodine will kill giardia and bacteria, but not cryptospiridia. Chlorine dioxide will kill giardia, bacteria and cryptosporidia, but you have to wait four hours, so it might be a good choice for when you're in the wilderness, and have a camp that you're sited at, where you have the time to wait. The makers of this product claim that it is similar to what municipal water companies use and that there is no chemical aftertase.

Good luck--and remember--don't drink the water unless you've treated it first.