I have a MultiPure under the sink filter system that had a new filter replaced a year ago. The filter is supposed to last through about 750 gallons of water (or something around there). Either way, I have used it for less than half that amount in the past year. The manufacturer says to replace the filter yearly, but they are expensive considering I don't use that much filtered water. (It was installed by the previous owners.)

Is it still safe to use filtered water through the existing filter until I really need to change it? Will it cause any harm?

Thanks for any help.