It would only be more pure based on what we can currently measure. Supposed we had tried this back when we just had to filter it for things we could <i>see</i> - the water would be clear and also likely still filled with cholera.<p>We know more about bacteria today, but can we filter for e.g prions?<p>Anyway the current system works, the new system might be better, but on the off chance that something goes wrong, why risk it?