DWR’s Proposed Residential Outdoor Water Use Standard
Updates from the 3rd Standards, Methodologies, and Performance Measures Workgroup Meeting on 6/30/21
Some of the items discussed below are no longer current. Please see the latest proposals from DWR on the WUE framework here.
On June 30th, 2021, the California Department of Water Resources (DWR) hosted the third workshop in an ongoing series of “Standards, Methodologies, and Performance Measures” meetings. The primary goal of these meetings has been to facilitate public engagement as DWR works towards an October 1st legislative deadline to determine a standard for efficient outdoor residential water use:
DWR, in coordination with the State Water Board, shall conduct necessary studies and investigations to develop recommendations for standards for outdoor residential water use that incorporate the MWELO. The standards shall apply to residential irrigable lands and include provisions for residential water features. (Source)
This outdoor water use standard (OWUS) is just one piece of the broader effort to implement SB606/AB1668, and like many of the other pieces of the implementation (indoor standard, landscape area measurement, water loss standard, CII dedicated irrigation standard, etc.) there are plenty of strong opinions to go around. And with residential outdoor water use likely to be one of the largest contributors to the overall water use objective, the State’s choice for the OWUS will have far-reaching implications for water use and efficiency in California for many years to come.
Important New Developments
There was a lot of information covered during the meeting, but three new developments stand above the rest in their importance.
Method for Calculating Residential Landscape Area
DWR is proposing that only irrigated area be counted toward the water use objective, although a buffer of 20 percent of irrigable-not-irrigated (INI) can be added in the case that a supplier fails to meet their water use objective. Let’s break this down a bit.
First, the choice to only use irrigated area came as a shock to many when it was discussed as an option back in February. For a long time, much of the analysis and discussion focused on irrigated + irrigable as reflecting the total landscape area of an agency, and this is still how many agencies think about landscape area, such as those with budget-based water rates.
Using only irrigated area doesn’t necessarily mean that every agency will receive a smaller water use objective, because as DWR has shown in their study, irrigated areas tend to have a higher evapotranspiration-adjustment factor (ETF) reflecting higher water use on irrigated lands. This higher ETF then means that the OWUS is likely to be higher if only irrigated area is considered.
However, using only irrigated area does have implications for which agencies will end up with higher water use objectives. Because of the way that the aerial image classification algorithm works, this will essentially mean that suppliers with lots of “green” area (when viewed from the sky) are likely to end up with a higher objective than those with lots of brown areas. This is especially important when some of those purportedly “not irrigated” areas actually ARE irrigated, which could be the case with some native landscaping that might appear unirrigated due to natural coloring, or just because of errors in the landscape area measurements.
Even DWR admits that some of the area that is currently being classified as INI appears as if it is actually being irrigated. This is the logic they propose for including a buffer of 20 percent of INI for agencies that don’t meet their objective. This also seems to be a way of coping with the fact that the legislation specifically mentions irrigable area, so using only irrigated area “ignores the legislative directive”.
Proposed Outdoor Standard
The other major announcement from the meeting was that DWR is proposing a residential outdoor standard of 0.7. This value is derived from their study data when averaging across several different model scenarios, and as such it reflects one estimate for the level of irrigation that is actually happening on the ground, right now.
Despite being an estimate of the current average level of irrigation, there are nevertheless some assumptions built into this number. One of these is the fact that the two “trimmed” scenarios assume that any agency with an observed ETF greater than one must be that way because of some sort of data or calculation error. This could be true, but since 25% of the modeled agencies have an ETF greater than one, it could be that they are actually reflecting the reality of on-the-ground irrigation, where irrigation efficiencies differ from MWELO ideals.
Effective Precipitation Will be Subtracted from ET
This is a more minor point and it has been discussed for a while now, but DWR doubled down on their desire to subtract effective precipitation from reference evapotranspiration before calculating the water use objective. One new development is that they propose to cap effective precipitation at 25% of total precipitation, and this is the scenario that informed their selection of the outdoor standard.
Some of the stated reasons for pushing ahead with the use of effective precipitation were to satisfy legislative requirements to use precipitation, along with a desire for more “spatial equity” between areas with high precipitation and those with low precipitation.
Looking Ahead
All of these developments are still just “proposed”, and there will probably be lots of public comment pushing back on pieces of this proposal, so we might still see some of these pieces change slightly. However, the vision that DWR has laid out so far for residential outdoor use is one that is substantially different from what some initially assumed back at the beginning of the framework implementation process.
It remains to be seen where suppliers in California will stand once all of the different pieces of the water use objective start to come together. Hopefully once all of the components are considered together, the end result will meet the goals of the legislation while still being fair and achievable for suppliers.
