As state water regulators consider extending drought restrictions though the fall, officials reported Tuesday that urban Californians had reduced their water use by 18.3% during December.
The savings, which are compared with December 2013 water usage levels, were the smallest in seven months of reporting and put California's cumulative savings at 25.5%, down from 26.3% in November.
Gov. Jerry Brown has called for a 25% statewide reduction in urban water use between June and February to help the state cope with a years-long drought.
With about a month and a half of reporting still to come, the state finds itself just squeaking by.
State Water Resources Control Board Chairwoman Felicia Marcus asked staff members whether they believed the state would meet the 25% mandate or whether it would be a "nail-biter."
Katheryn Landau, who presented the December data, responded that she was "cautiously optimistic."
"We're in field goal range, but you want a touchdown," Marcus said.
She added later: "The fact that we're focused on those percentages is, I think, less important than that people have really stepped up ... sometimes at extraordinary cost."
Marcus and other water officials have said they expected savings to be lower during the colder, wetter months, when people typically use less water anyway and there is less room to cut back.
Still, the December savings effort marked the third consecutive month that Californians collectively failed to meet Brown's goal of a 25% cutback.
To hit that target, the water board assigned conservation standards to each of the state's 411 urban suppliers last year.
Suppliers with a history of high per capita water use were ordered to cut as much as 36% from 2013 totals. Suppliers with a history of lower consumption were told to cut as little as 4%.
Some have struggled to meet their targets, repeatedly falling five, 10 or even 15 percentage points short. In October, regulators fined four suppliers $61,000 for noncompliance, and they have said that more penalties could be forthcoming for suppliers that don't shape up.
Many of the hardest-hit districts have complained for months that their individual targets failed to take into account local conditions. So last month, state water board staff unveiled a modified set of drought rules that would provide suppliers with some relief.
The proposed changes to California's emergency drought regulation reward water districts for investing in new local supplies and allow for adjustments to savings goals based on a district's climate and population growth. The proposal allows water providers to have the so-called conservation standards reduced by as much as eight percentage points.
Collectively, officials said the adjustments and credits could drive statewide water savings below the 25% target.
Water board staff members have characterized the changes as "modest" and an attempt to be flexible in responding to water suppliers' concerns.
But environmental groups have criticized the credits and adjustments, saying they seem to have been created to satisfy a small number of water suppliers who wanted some slack.
"I just think they're inappropriate in the middle of an emergency," said Sara Aminzadeh, executive director of the California Coastkeeper Alliance, which advocates for clean water. "It just sends the wrong message."
"Californians have been asked to reduce and they stepped up to the plate," she said. "Then nine months later … to offer these adjustments and credits is potentially confusing and undermines what we've done over the past year."
Depending on how much rain and snow the state gets this winter, officials have said they could revisit the rules in March or April. They could adjust or even eliminate the restrictions at that time. A strong El Niño has already delivered some rain to California, and meteorologists say they believe more will come in February and March.
Later Tuesday, officials from the California Department of Water Resources are scheduled to take measurements of the snowpack at a station about 90 miles east of Sacramento.
Electronic readings of the statewide snowpack on Tuesday morning showed water content was 20 inches, or 114% of the historical average for that date, according to the California Department of Water Resources.
Officials have cautioned, though, that while a healthy snowpack can make a dent in the drought, it would need to be about 150% of average by April 1 to have a shot at ending the drought.
The state's current drought regulations are scheduled to expire next week and the water board is to consider the proposed rule changes later Tuesday afternoon. If approved, the updated regulations would be in effect until October.
For more on the California drought and water, follow me on Twitter @ByMattStevens