Abstract: Potable (drinking) water systems of recreational vehicles, boats, vacation homes, and the like, need to be protected against freezing during periods of non-use during the cold winter season. Typical propylene glycol antifreeze additives are effective but expensive. It has been found that use of an inhibitor solution based on food-grade corn syrup effectively boosts the effectiveness of propylene glycol so that as little as 19% plus or minus 0.25% by liquid volume is optimally used together with about 10% of a food-grade corn syrup in an anti-freeze solution for -50% protection. This is a more economical and effective system than previously known in commercialized systems heretofore maintained as trade secrets by the inventors and the assignee.