The old custom of sprinkling water with a ladle or by hand on the ground, called “uchimizu”, is a well-known example of the use of water in Japan’s daily living. People used to sprinkle water in their house entrances and gardens or in front of their shops to lay the dust and ease the heat3, which sometimes implies welcoming of guests.
Mission Uchimizu was launched as a great social experiment in 2003 in order to prove the hypothesis that we can lower the summer temperature by two degrees Celsius if one million people simultaneously do uchimizu (sprinkle water) on streets and gardens4.
- Taisho, regarded as the hottest day of the year on the lunar calendar
- Shosho, regarded as the day the summer heat begins to ease
- Water has a high heat of vaporization. As sprinkled water evaporates, it takes heat away from the ground.
- Mission Uchimizu has become a social action that millions of people in Japan take part in and doing uchimizu through the summer every year.
How to join
-
Practice uchimizu
How to do uchimizu
every
sunny day. -
Uchimizu Day
See the details
(August 1st) -
Practice uchimizu
See the details
when the shops are opening.
Warning: Preventing
Heat-related Illness.
Schedule uchimizu carefully and pace yourself.
Get enough water and replace salt & minerals to stay hydrated!
Please visit the following websites for more information on how to prevent heat-related illness.
Heat Stroke Alerts in Japan,
Ministry of the Environment of Japan
Tips for Preventing Heat-Related Illness,
Centers for Disease Control and Prevention (CDC), U.S. Department of Health & Human Services
The day-long mission
We call on you to practice uchimizu at home or in other places where you are, as often as possible from morning till night on August 1st rather than just once a day!
*Postponed in case of stormy weather.
How to do uchimizu
When the water you sprinkle has dried up, sprinkle more.
The air temperature will be lowered by the evaporation of sprinkled water. When the sprinkled water has dried up, the temperature no longer goes down. When the water you’ve sprinkled dries up, sprinkle (uchimizu) more! Roll up your sleeves and do uchimizu time and time again.
Lowering the temperature on August 1st
Can we make the air temperature on the day lower than the forecast of the previous day? Let’s cool off on a hot summer day by sprinkling water!
Express your intention to join & share your experience after uchimizu on social media using the hashtag #uchimizu and #打ち水大作戦.
