ET Hotline



Coastal, Central and Foothill weather station data is electronically transmitted daily to IRWD where it is used in a formula to calculate evapo-transpiration, also known as ET, which is the amount of water needed by turfgrass to remain healthy in each specific climate zone.

Outdoor watering accounts for 40 to 70 percent of water used in Orange County. With thousands of acres of valuable community parks, gardens and greenbelts within its boundaries, IRWD's billing system relies on accurate weather station data to provide landscape and commercial customers like you with site-specific budgets to ensure that your landscaping receives sufficient water.

Important Links

Experiencing technical issues with links below? Please call ET hotline (949-453-5451 for English and 949-453-5452 for Spanish) for potable and recycled water weekly budgets.

Daily ET Report link

Recycled Weekly Report link

Potable Weekly Report link

CIMIS Information

MAP: Evapotranspiration Zones + Weather Station Locations

*Weekly ET data should be up to date by Monday at 10:30 a.m. PT.


 Historical ET Data

      Most recent

2022  |  2021  |  2020


2019  |  2018  |  2017  |  2016  |  2015  |  2014  |  2013  |  2012  |  2011  |  2010


2009  |  2008  |  2007  |  2006  |  2005  |  2004  |  2003  |  2002  |  2001  |  2000


1999  |  1998  |  1997


Weather Determines Your Water Budget



How Weather Affects Your Water Budget: When the weather is hot or windy, your budget goes up automatically. When it's cool or rainy, your budget decreases.

Staying Within Budget Makes Sense: The goal is to allow you the correct water budget you need for your landscape to stay healthy and attractive. Using more water than plants need is a waste of water, a waste of your money, leads to unhealthy plants, and can contribute to pollution-causing urban runoff.


Weather Station Technology Helps You Save Water



Advanced Weather Station Technology:
IRWD uses the most advanced weather station technology, consisting of Campbell Scientific CR-10X Data Logger equipment, the same used by the California Department of Water Resources for the 100 California Irrigation Management Information System stations around the state.

IRWD's Three Microclimates: Within our service area, there are three distinct microclimates, known as the Coastal, Central and Foothill zones. IRWD maintains a separate weather station in each climate zone to monitor exact wind and weather conditions, including air temperatures, relative humidity, precipitation, solar radiation, and wind direction and speed.