Hello Coolkat:
This is a direct cut and paste quote from the 2016 Greenstone, the official park newsletter
Drinking Water
Potable water is only available in Rock Harbor and Windigo. All surface lake and stream water should be considered contaminated with pathogens. Drinking contaminated water can make you very sick. Water collected in the park should be boiled at a rolling boil for at least one minute or passed through a 0.4 micron filter. To be assured of no risk of contamination from small bacteria and viruses, all filtered water should be further treated with iodine or other approved chemical methods. By itself,chemical treatment is not an effective method of water purification. If you boil your water, bring plenty of stove fuel. If filtering, bring a replacement cartridge for filters that cannot be cleaned in the field. Please note: SteriPENs and other UV purifiers have not been manufacturer-tested for a common Isle Royale parasite and cannot be considered effective.
I've never heard of any new requirement of 0.2 micron. Smaller is better but both will remove the tapeworm eggs and neither will remove viruses or some smaller bacteria.
Search the entire forum using the keyword "tapeworm" in this link below and you will find many discussions centered on the parasite of which you speak.
Forum Search for Tapeworm
Steripens definitely will not remove tapeworm eggs that could reside in any water on the Island. If ingested you won't know about it until many years later, as you will be performing a stand-in role of the moose where cysts grow in any of the internal organs mostly commonly the lungs but also the brain.
To be assured there are no pathogens ingested that are smaller than 0.4 micron such as small bacteria and all viruses, it is recommended to use additional treatment (chemical or UV). I used to drink directly from Lake Superior but after the recent report and discussion regarding
Swimmer's Itch, I don't think I want to take even the remotest chance of ingesting that parasite.