Bathwater reuse can save households 8,280 yen annually

A comparison of household utility costs reveals that reusing bathwater through reheating (re-heating/re-circulating) can lead to significant savings compared to replacing water daily. For a standard 180-liter bath, replacing the water every day costs approximately 108 yen per session in combined water and gas fees, totaling about 3,240 yen per month.

By reusing the water and only paying for the gas required to reheat it, the monthly cost drops to approximately 2,550 yen. This method can save a household roughly 690 yen per month, or approximately 8,280 yen per year.

However, hygiene remains a critical concern. Research from the Japan Hygiene Microorganism Research Center indicates that bacteria levels in bathwater can increase by thousands of times overnight if left sitting. To balance cost savings with health, it is recommended to use leftover bathwater for secondary purposes such as laundry or cleaning rather than leaving it in the tub.