Boiling
Boiling is the simplest and most straightforward method of killing or inactivating most pathogens that may be present including Cryptosporidium, provided one has plentiful time and fuel! However boiling will not remove suspended impurities or chemical contaminants. Many find it leaves a “flat” taste in the water, and waiting for the water to cool can be tiresome. However a safe low initial cost system could be a simple pre-filter (to remove suspended impurities) with a carbon filter (to remove odours & chemicals) and then bringing this filtered water to a rolling boil for 1 minute to kill the germs.
Sedifilt brochure