The traditional East Asian calendars divide a year into 24 solar terms. Yǔshuǐ, Usui, Usu, or Vũ thủy is the 2nd solar term. It begins when the Sun reaches the celestial longitude of 330° and ends when it reaches the longitude of 345°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 330°. In Gregorian calendar, it usually begins around 18 February (19 February East Asia time) and ends around 5 March.
Pentads
Date and Time (UTC)
| year | begin | end |
| 辛巳 |
2001-02-18 14:27 |
2001-03-05 12:32 |
| 壬午 |
2002-02-18 20:13 |
2002-03-05 18:27 |
| 癸未 |
2003-02-19 02:00 |
2003-03-06 00:04 |
| 甲申 |
2004-02-19 07:50 |
2004-03-05 05:55 |
| 乙酉 |
2005-02-18 13:31 |
2005-03-05 11:45 |
| 丙戌 |
2006-02-18 19:25 |
2006-03-05 17:28 |
| 丁亥 |
2007-02-19 01:08 |
2007-03-05 23:18 |
| 戊子 |
2008-02-19 06:49 |
2008-03-05 04:58 |
| 己丑 |
2009-02-18 12:46 |
2009-03-05 10:47 |
| 庚寅 |
2010-02-18 18:35 |
2010-03-05 16:46 |
| 辛卯 |
2011-02-19 00:25 |
2011-03-05 22:29 |
| 壬辰 |
2012-02-19 06:17 |
2012-03-05 04:21 |
| 癸巳 |
2013-02-18 12:01 |
2013-03-05 10:14 |
| 甲午 |
2014-02-18 17:59 |
2014-03-05 16:02 |
| 乙未 |
2015-02-18 23:49 |
2015-03-05 21:55 |
| 丙申 |
2016-02-19 05:33 |
2016-03-05 03:43 |
| 丁酉 |
2017-02-18 11:31 |
2017-03-05 09:32 |
| 戊戌 |
2018-02-18 17:18 |
2018-03-05 15:28 |
Source: JPL Horizons On-Line Ephemeris System
Each solar term can be divided into 3 pentads (候). They are first pentad (初候), second pentad (次候) and last pentad (末候). Pentads in Yushui including:
- China
- First pentad: 獺祭魚, 'Otters make offerings of fish'. As fish begin to swim upstream, they are hunted by otters, which are believed to offer the fish to heaven.
- Second pentad: 鴻雁來, 'The wild geese arrive'. Wild geese begin to make their northward migration, following the onset of spring.
- Last pentad: 草木萌動, 'Trees and grass put forth shoots'.
- Japan
- First pentad: 土脉潤起
- Second pentad: 霞始靆
- Last pentad: 草木萠動