Generally speaking from the human standpoint as the definitive host, the infective stage, in this case an egg (different infective stage compared to flukes) of the Hydatid tapeworm (Echinococcus granulosis and 3 other species) and all tapeworms eggs which humans shed in their stools, for that matter, are very highly resistant to dessication, chemical disinfection, and UV-C sterilization. IIRC, heat/boiling will do them in though. Basically, nothing the hiker will carry will kill the infective stage. It must be prevented from entering the water that will be drunk by means of filtration. You've got the size right, IIRC. I'd go a little smaller, like 20 microns for safety purposes, but perhaps I'm just being overly cautious.
As far as how a human generally gets infected with Hydatid tapes, here is how it occurs to the best of my recollection (its been over 30yrs since i studied parasitology, so you may want to verify this info):
0) wild canines or feral dogs get infected from eating infected animals like sheep, goats, cows, and also, wild herbivores like deer, moose, roos, etc.
1) infected canine defecates in water or run-off carries fecal matter and Hydatid eggs into a water source.
2a) a hiker drinks the unfiltered water from that contaminated source and ingests some eggs.
2b) the shepherd transfers eggs from their sheep/shepherd dog *BEEP*/fur/anal region to their lips/mouth via their fingers or an inanimate object. Possibly also, allowing an infected dog to lick your hands (and forgetting to scrub them good), or your lips (remember dogs have a penchant for licking their hintermost parts). I never let any dog lick my face and always wash my hands after they lick my hands or I pet them.
Flatworms have a complex life cycle with different stages. NOT ALL stages are capable of infecting the same species. "Different strokes for different folks", so to speak.
Ok, now here's the point you may want to verify. I'm not sure that eating infested, undercooked animal flesh will give us the infection. It's the wrong life cycle stage, IIRC - but, please verify this, but I don't recall that humans can be infected this way - IN THE CASE OF HYDATID TAPES - other parasites yes, e.g. Trichina spiralis, Taenia solium, etc. Definitely, contaminated water can lead to infection. Symptoms of the infection may not show up for up to 20yrs. As you are already aware, these little guys are different from the more common beef, pork, and fish tapeworms. They're very small and they leave the intestines and infect the liver, lungs, and brain, and possibly other organs (I'm forgetting now).
You're right. Don't mess with these little buggers. 12-18mos ago G.R., on these Forums alerted me to their presence at Isle Royale - didn't know, at the time, that Hyadatid tapes were also indigenous to that Park.
Enjoy Greece. We'll be here when you get back. Hope you don't mind sharing your adventures with us.