Instruct: Classify Amazon reviews into positive or negative sentiment
Query: It works.

We live in the Ozarks, out in the woods and our well has very hard water with a lot of minerals. If I make coffee straight from the tap, the coffee has a scummy film on it. When I use filtered water, coffee tastes better and no scum. I've never had any filters with indicators on them but within 5 weeks I notice the water is filtering much more slowly. If I don't get a new filter in right away, I start to notice a film on the coffee... seems obvious that it's time to change as soon as I notice it going slowly.