Actually, I asked the people who developed the AquaStar UV system and they provided research that showed the UV treatments successfully scrambled the helminths DNA so they were unable to pose a health risk to humans. The bodies were of course still in the water but inert. I believe they have their data public at www.uvaquastar.com
I couldn't find the information at their web site. Anyway, there is a distinction between the adult helminthes and their eggs. Killing the adult helminthes is easy. Chlorine, chlorine dioxide, UV, iodine, heat--anything should kill the adults, because they are soft-skinned. But killing the eggs of echinococcosis and similar helminthes is another matter. These eggs are designed to lie on the ground (where the canine predator defecated) for months or years until the herbivore prey (sheep, mice) accidentally ingests the egg while eating grass. The eggs will thus be exposed to natural UV light for long periods of time. I would imagine the eggs are also resistant to chemicals, simply because cryptosporidium and giardia cysts are, which suggests that putting a chemically resistant shell around an egg is not that difficult in biological terms, and is probably easier for the helminths given that their eggs are much larger than the cryptosporidium and giardia cysts and hence probably sturdier. But this is speculation on my part.
Eating the adult form of helminthes is known to be an issue when you eat uncooked vegetables that grow in moist environments. Liver flukes, in particular, are known to be a problem with watercress.
Another thing. Just because hydatid cysts from echinococcosis worms is not common in the US or Australia or other areas where these worms exist, does not mean there isn't a problem for backcountry hikers. Remember, most people in the United states and Australia never visit the backcountry and hence are never exposed to the problem. But the problem does exist. As my link above indicates, when the backcountry visits the people in cities (foxes in Munich), echinococcosis does indeed become a problem for the population as a whole. The real question is what is the incidence of hydatid cysts for hikers who travel in areas like the Arctic or Lake Superior region of North America, or the Alps in Europe AND drink water from streams without filtering (by filtering I mean just that, not chemical or UV treatment). Given that it takes from 10 to 30 years for problems to occur, it can be quite difficult to get reliable information about this.
Finally, just because the dogs are treated in Australia does mean the echinococcosis problem is eliminated. There could also be wild predators of sheep (dingos? coyotes?) which carry the worms and so the worm circulate that way. And it doesn't just have to be dogs/coyotes and sheep. In the European Alps, for example, the worms are carried by foxes and mice rather than dogs and sheep. In the North American Arctic and Lake Superior region, it is wolves and caribou/moose/deer.