Woodside, Portola Valley and Atherton water customers cut their use by 40 percent and more in June compared with June 2013, according to numbers released by the towns.
The towns are in the California Water Service Company's Bear Gulch Water District, which has been ordered by the state to cut water use by 36 percent from 2013 levels. That mandate went into effect in June.
In its latest reports for these communities, Cal Water also revised significantly the numbers originally reported for May. Asked to explain the revisions, Cal Water spokesman Justin Skarb said the company is used to system-specific rather than community-specific reporting on water consumption, and that the numbers for the local reports were incomplete.
"The (software) error was fixed in the most recent report, which is why 2015 numbers changed," Mr. Skarb said. The company is also rerunning numbers for 2013 and 2014, he said.
"We are in the process of updating each of the reports, and hope to have them to the cities in the near future," he said. "We truly apologize for the confusion."
While year-to-date numbers are provided here, the measure of whether water suppliers are meeting state mandates starts with the month of June and extends through February 2016. Therefore, year-to-date and May numbers are not relevant in determining whether water suppliers are meeting the mandates.
In June, Portola Valley customers led the way in the Bear Gulch District, reducing usage by 48 percent, or 30.7 million gallons, compared with June 2013. The town's year-to-date reduction is 17 percent.
Woodside customers reduced their consumption by 45 percent, using 45.3 million gallons less than in 2013. Water use is down 12 percent for the year to date.
Atherton customers used 57.5 million gallons less than in June 2013, a savings of 40 percent. The town's consumption is down 2 percent for the year to date.
The Menlo Park Municipal Water District, which has been ordered by the state to cut water use by 16 percent from 2013 levels, purchased about 78 million gallons of water from the San Francisco Public Utilities Commission in June, down about 24 percent from June 2014 purchases, according to Pam Lowe, senior civil engineer with the city of Menlo Park
As a whole, the Bear Gulch District, which also includes parts of Menlo Park and Redwood City, lowered consumption in June by about 41 percent from 2013 levels, and by 23.5 percent for the year to date, according to Ms. Smithson.
The statewide goal is a 25 percent reduction. For May, the State Water Resources Control Board reported a statewide drop in consumption of 29 percent. Numbers for June are not expected until late July, water control board spokesman George Kostyrko said.
The local weather in June was not significantly different from the weather in June 2013. The mean temperature in Menlo Park was 68 in June 2013 and 67 this year, according to data from Weather Underground.
The data shows a maximum of 12 days in June 2013 for which air conditioning was called for versus 16 days this year.
Weather conditions affect the rate at which irrigation water evaporates into the atmosphere, according to Kevin Kielty, an arborist based in San Mateo. Water evaporates more quickly as the temperature goes up.
Native trees, such as valley oaks and coast live oaks, are adept at accumulating rainwater and using it throughout the year, Mr. Keilty said. "They're doing quite well," he said of the area's oak trees.
Not so for non-natives such as pine, birch and magnolia. Pines have the bark beetle to contend with along with the drought, and birches and magnolias depend on water used to irrigate lawns, he said.
Peninsula redwoods are also struggling because they're out of their native foggy habitat on the coast, he said. "(Redwoods) require a lot of surface water," Mr. Keilty said. "They should be getting fog-belt rain every single day."
May numbers revised
In its water consumption reports for Bear Gulch District towns for June, Cal Water revised previously reported numbers for May.
The revised numbers are as follows:
■ Woodside customers cut water consumption in May by 28 percent compared with May 2013 (not the 24 percent previously reported) and have used 7 percent more water during the first five months in 2015 (not 19 percent less).
■ Portola Valley customers cut back by 29 percent in May (not the 36 percent previously reported) and consumed 1 percent less water from January through May (not 11 percent less).
■ Atherton's May 2015 use was unchanged from 2013 (not lower by 15 percent) and up 22 percent for 2015 (not up the 4 percent originally reported).