# R04 Method Specification v1.0

## 1. Unit of analysis

A declared data-center / compute expansion scenario in a defined water-service and watershed context. Compute capacity is expressed as **IT load (MW)**. Direct site water is expressed as **million gallons per day (MGD)**. The method does not silently convert facility nameplate, grid interconnection, utility service, or campus load into IT load; the declared IT-load basis must be explicit.

## 2. Evidence classes

- **E1 — directly reported:** utility- or agency-reported observations and capacities.
- **E2 — official modeled / synthesized:** official studies whose assumptions are published.
- **E3 — external research / benchmark:** peer-reviewed, laboratory, academic or public-dataset context.
- **E4 — Critical Load analytical assumption:** transparent scenario choice introduced for screening; never presented as an observed fact or official threshold.

## 3. Core quantities

For project IT load `P_MW` and water-use parameter `WUP` in gallons/day/MW:

`Direct water (MGD) = P_MW × WUP / 1,000,000`

The release uses official ICPRB bounding scenarios:

- Low: 600 gpd/MW average; 2,100 gpd/MW maximum-day
- Medium: 800 gpd/MW average; 2,900 gpd/MW maximum-day
- High: 1,400 gpd/MW average; 5,200 gpd/MW maximum-day

A separate 8,500 gpd/MW peak sensitivity represents the high end of nominal evaporative-site values reported by ICPRB; it is not the regional high scenario.

## 4. Peak Water Capacity Screen (PWCS)

The PWCS is intentionally a **screen**, not a water-right or service-availability model.

Let:

- `C_future` = declared future maximum-day system capacity (MGD)
- `a` = analyst-declared fraction of that capacity allocated to data-center potable peak demand
- `D_DC,peak,current` = current published data-center potable peak demand (MGD)
- `I_peak` = peak water intensity of the selected scenario (MGD/GW)

Then:

`Incremental potable budget B = a × C_future − D_DC,peak,current`

`Screened added IT capacity P_screen = max(0, B / I_peak)`

For the illustrative v1.0 screen: `C_future = 90 MGD`, `a = 16%`, `D_DC,peak,current = 8 MGD`, so `B = 6.4 MGD`.

This yields approximately:

- Low: 3.05 GW
- Medium: 2.21 GW
- High: 1.23 GW
- 8.5 MGD/GW facility-high sensitivity: 0.75 GW

**Interpretation:** these values show the consequence of a declared allocation rule. They do not establish the allocation rule.

## 5. Two-ledger source / consumption treatment

For project direct water `D_total` and reclaimed-water share `r`:

`Potable burden = D_total × (1 − r)`  
`Reclaimed supply = D_total × r`

With consumptive factor `c`:

`Estimated hydrologic consumption = D_total × c`

The v1.0 default uses `c = 75%` only because that factor is used in the cited ICPRB regional analysis. Project-specific cooling cycles, blowdown, discharge and seasonality can change it.

Thus increasing reclaimed share can reduce potable-system burden without necessarily reducing total direct evaporative consumption by the same amount.

## 6. From PWCS to a Water-Constrained Compute Envelope (WCCE)

A verified WCCE should be calculated only after defensible project-specific limits can be expressed on the same IT-load basis:

`WCCE(s) = min(P_potable, P_reclaimed, P_basin, P_wastewater, P_regulatory, ...)`

Only quantitatively defensible limits enter the minimum operator. Other conditions remain explicit gates rather than fabricated numeric limits.

Minimum evidence for a verified project-level result includes: utility will-serve / hydraulic evidence; cooling design and seasonal WUP; source split; wastewater/blowdown path; watershed/low-flow conditions; emergency/drought rules; project phasing; and independent water-domain review.

## 7. Uncertainty and sensitivity

The public model exposes rather than hides uncertainty. At minimum, a user should vary:

- cooling / WUP scenario;
- project MW;
- reclaimed-water share;
- data-center allocation fraction;
- consumptive factor;
- project phasing / peak coincidence.

The current release uses deterministic sensitivity rather than a probability distribution because a defensible parameter distribution has not yet been established from public evidence.

## 8. Non-goals

v1.0 does not claim a groundwater/surface-water rights allocation, a final regional carrying capacity, a drought operating rule, a project-specific permit result, indirect electricity-related water, or a peer-reviewed causal model of community impact.