*3.3. Performance Indicators*

The percentage of local water supply is defined as the fraction of water demand that is met by cumulative supplies from groundwater, stormwater capture, NPR, IPR, and future conservation. For the projection years (i.e., 2020–2050), volumes of conserved water are included in local water supply percentage calculations because the projected demand for future years does not account for future conservation measures. However, the historical average year is an exception where the water demand value is based on real water consumption data, and therefore, the local water percentage excludes conservation.

Daily water use per person (in the units of liters per person per day, *L*/*P*/*D*) is used as an indicator for water demand (note that water demand excludes volume of water for beneficial reuse). Two energy indicators are defined, one to capture the electricity demand intensity of the water system in kWh/m3, and the other to track annual electricity demand for water supply per person in kWh/P.

We also estimate emissions per unit of water demand in kgCO2/m3. Total carbon dioxide emissions are estimated using an emissions intensity of 225 kgCO2/MWh, which represents California's 2018 electric grid [39], and 75 kgCO2/MWh, which was applied as a proxy for a future decarbonized grid mix based on [40]. For a future decarbonized grid in 2035, we calculated the average emissions intensity of California's electricity system based on information provided in [40] for the electricity generation fuel mix and total CO2 emissions in 2030 and 2040. For the state of California to achieve an 80% reduction in California's greenhouse gas emissions by 2050 (from the 1990 levels), the high electrification pathway assumes that the share of renewable energy sources in California's electricity supply is 60% and 79% in 2030 and 2040, respectively [40], which illustrates significant growth from the share of renewables in 2018, i.e., 29% based on [39].

#### *3.4. Decomposing Driving Factors for Electricity Demand*

An index decomposition analysis (IDA) is formulated to examine the impact and significance of key factors influencing the electricity demand for LADWP's water system over time. We define influencing factors, including population, water use (influenced by water demand and water conservation programs), and the energy intensity of water supply portfolios. We reformulate Equation (2) to describe the relationship between the three predefined influencing factors and the total electricity demand for the water system:

$$E^t = P^t \times \frac{V^t}{P^t} \times \frac{E^t}{V^t} = P^t \times \frac{V^t}{P^t} \times EI^t = P^t \times \frac{V^t}{P^t} \times V^t \sum\_{i}^n \sum\_{j}^m EI\_{i,j} v\_j^t \tag{2}$$

where *Et* is electricity demand for water, *P<sup>t</sup>* is population, *V<sup>t</sup>* is volume of water supplied (water supplied is equal to projected water demand minus projected conservation), *vtj* is the fraction of water supplied from source *j* in year *t*, *EIi*,*<sup>j</sup>* is energy intensity of water supplied from source *j* in water supply stage *i*. A change over time in electricity demand can be decomposed into three driving factors relating to the effects of population, physical water supplied per person, and the energy intensity of water supply as it is shown in Equation (3). Here, we apply the most common decomposition method, i.e., additive logarithmic mean Divisia index method I, from [41], to calculate Δ*EP*, Δ*EV* and Δ*EEI* shown in Equations (4)–(6), where *<sup>L</sup>*(*<sup>x</sup>*, *y*)=(*x* − *y*)/(*lnx* − *lny*) for *x* = *y*, and *<sup>L</sup>*(*<sup>x</sup>*, *y*) = *x* for *x* = *y*. We conduct decomposition analysis of total electricity demand change in year 2035 and the reference historical average (Δ*E* = *Et*=<sup>2035</sup> − *ERef*), and we repeat the analysis for all four studied scenarios.

$$
\Delta E = \Delta E\_P + \Delta E\_V + \Delta E\_{EI} \tag{3}
$$

$$
\Delta E\_P = L(E^t, E^{Ref}) \times \ln(P^t / P^{Ref}) \tag{4}
$$

$$
\Delta E\_V = L(E^t, E^{Ref}) \times \ln((V^t/\mathcal{P}^t)/(V^{Ref}/\mathcal{P}^{Ref})) \tag{5}
$$

$$
\Delta E\_{EI} = L(E^t, E^{Ref}) \times \ln(EI^t / EI^{Ref}) \tag{6}
$$
