Pinnacle™ or Pinnacle Plus™ reverse osmosis filters work well between 77º and 113º Fahrenheit (25º–45º Celsius). Reverse osmosis membranes work best using colder water. The colder the source water is the higher the pressure and the lower the flow will be through the reverse osmosis membrane. As such, more impurities or Total Dissolved Solid (TDS) are removed from the source water. The higher the temperature of the source water is the lower the pressure and higher the flow will be through the reverse osmosis membrane. As such, more impurities are able to pass through the filter. The difference is minimal in any case but worthwhile noting.