Of course, every filter in the world relies upon the quality (or not) of the input water and so we can’t say that the filter will last to 3,600 litres with any certainty. Because we’ve used the highest quality filter media in the world, we know that it will last way beyond 3,600 litres but it’s always the amount of ‘crud’ a filter retains that determines the ultimate lifespan, and this will be evidenced by a slowing down of flow until it stops. If you continue to try to get it to run after it stops either the hose will blow off the unit or the case will crack open. Neither of these happenings are a cause for concern, but some customers like to have a new filter ready anyway so they have no wait for a newly ordered filter to arrive.
You can order a new UltraStream replacement filter here