ZeroWater's Ion-exchange resin filters are a reliable and efficient way to get delicious, filtered water. They work by exchanging ions in the water with regenerated ions from the resin beds, which can remove a variety of contaminants from water, including lead, nitrates, sulfates, calcium, magnesium, and other heavy metals. The exchanged ions bind with the contaminants, making them much easier to filter out. Our combination of cation and anion exchange resins can reduce 99.6% of dissolved contaminants in your water. However, when the filter is exhausted no more contaminants can be filtered out and an unpleasant smell and taste may be present. This is a common cause of overuse and can also occur by pouring hot water into the filter or freezing it. Be aware, though, that while the smell is unpleasant, it does not indicate any harm or danger. It is only time to replace your filter. Change your filter once the TDS meter reads 006.