I've used the Micro-Pur recently but they are kind of spendy. Seems like Aquatabs are used worldwide except for the states. Are they essentially the same thing?

Really? 44 views and no one knows anything about these?

Heard of them, but that is it. Sorry can't help ya'

Are you trying to goad people into responding no? Okay, never used em.

Safety ain't always cheap. I use the SteriPen and micropur tablets.

Doug Ritter discusses Aquatabs and similar Chlorine based methods (along with other methods) here : http://www.equipped.org/watrfood.htm#WaterProcurement.

Hey, thanks Yucca. I should have known Doug would have some info on the main site. I know Aquatabs are used all over the world but there's little info on their use in the States.

In the USA Aquatab is the name of a drug for treating congestion and coughs.
Aquatabs as used in the rest of the world are a solid chlorine type tablet. One tablet per liter.
I have no idea on the exact ingredients, Micropur are chlorine dioxide tablets.

Aquatabs says they are:

so they should do the same job.

Aquatabs are not effective against Cryptosporidium Oocysts.

Those are quite tough bastards. Here the options for killing crypto:
Ammonia (5%, 30 min, 22 °C, 97% reduction),
hydrogen peroxide (7.5%, 20 min, 20 °C, >3 log reduction),
heat (72.4 °C, 1 min; 64.2 °C, 5 min),
ozone (12 mg/L*min, 20 °C, 3 log reduction),
UV (254 nm, 22 mJ/cm^2, 4 log reduction),
Solar irridation (830 W m^2, 40 °C, 10 h (30 kJ)),
Gamma irridation (400 Gy),
Chlorine dioxide for 3 log reduction (water temperature, mg/L*min Chlorine dioxide): 1 °C, 1830; 10 °C, 830; 20 °C, 347).

Of these, I'd say UV, heat and Chlorine dioxide are the most sane options for you.

I see you're in Finland. What sort of issue is crypto in the Western United States?

Here data from around the world:

LeChevallier et al. (1991a) examined 66 source water supplies in 14 states and 1 province in Canada. Sources were characterized as protected from or impacted by industrial pollution. Of 85 samples collected, 87.1% were positive for oocysts, with concentrations ranging from 0.07 to 84/L.
...
McTigue et al. (1998) conducted a year-long study of 100 surface water treatment plants in the United States, examining raw and treated drinking water. Cryptosporidium was detected in 77% of the raw water samples and in 15% of the treated water samples. In raw waters, oocyst levels ranged from 0.5 to 117 per 100 L and in finished drinking water the levels were 0.04 to 0.8 per 100 L.
...
In Germany, source waters at six water treatment plants the average number of oocysts was 116 per
100 L; in finished drinking water, 29.8% of 47 were positive for Cryptosporidium (Karanis et al., 1998).
...
In Asia, Hsu et al. (1999) found high levels of oocysts in the watershed area and the Kau-Ping River,
which serves 2.5 million people in Taiwan. Raw water samples (75% positive) were as high as 12,516
oocysts per 100 L at one site, whereas treated drinking water levels (40% of samples positive) were
reported as high as 159 oocysts per 100 L.
In Hong Kong, in the Lam Tsuen River, oocysts were found
at one of four sampling sites each at concentrations of 3 to 30 per 10 L; along the Shing Mun River, a
single site was positive for Cryptosporidium once with 13 oocysts per 10 L (Ho and Tan, 1998).
...
In Israel, 80% of 15 samples from five streams were positive for Cryptosporidium with an average
concentration of 0.04 to 1.9 oocysts per liter (Zuckerman et al, 1997).
...
About North American Watersheds:
"The results suggest that most surface water systems would require, on average, a 3-log reduction in source water Cryptosporidium levels to meet potable water goals."
http://aem.asm.org/cgi/content/abstract/69/2/971