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Rate-Shock Affordability Modeler: CES Budget-Share Calculator for Water Rate Cases

A calculator for water companies to see how a price increase affects a household's budget for other essentials.

An Excel-native calculator for water utilities and regulators that applies the paper's closed-form CES/Cobb-Douglas demand functions to a proposed rate increase, showing how a household's spending shifts between water and other essentials. Affordability analysis becomes plug-in algebra with two inputs instead of an econometric modeling project.

EngineeringOptimization and Mathematical Programming
Urban Stormwater and Fluid ManagementWater utility regulation — rate-case affordability and demand-response analysis

Concept

A single-purpose tool for utility rate proceedings. Inputs: a representative household's income, its current water budget share (readily available from utility billing data), and one dial — the CES elasticity of substitution between water and all other goods, set from published ranges. When a rate case proposes a price change, the calculator applies the paper's closed-form demand functions and reports, per income decile: new water consumption, new water budget share, and the dollar crowd-out of spending on other essentials. The wedge is transparency and auditability: because the paper shows these demands follow from elementary algebra rather than calculus or statistical estimation, every output number traces to a formula a hearing officer can check, and the whole model lives in the spreadsheet environment where rate filings are actually written.

Why now

The new paper [0] establishes that Marshallian demands for CES utility (with Cobb-Douglas as a special case) can be derived and evaluated without calculus — meaning a household's response to a price change is a closed-form formula, not a fitted econometric model. That converts household-level affordability analysis from a research project into a two-parameter calculation (budget share plus substitution elasticity) that a rate analyst can run and defend in Excel. This lands exactly where the theme's evidence sits: the catalog's tariff work shows water-system sustainability requires full-cost-recovery pricing, but the open question for any proposed tariff is what it does to household demand and burden — this tool supplies that missing demand side, and the non-calculus derivation keeps it explainable to non-technical stakeholders in public hearings.

Written by GLM · 12 Oct 2026

AI assessment

Backed by 1 paper92

A highly focused, low-friction tool that converts a theoretical microeconomic derivation into a practical regulatory audit tool for water affordability.

Evidence strength
5/5
The idea directly applies the paper's core contribution—the non-calculus closed-form solution for CES demand—to a specific real-world calculation.
Market pull
4/5
Utility regulators and consumer advocates have a high, recurring need for defensible affordability metrics during rate cases.
Novelty & moat
4/5
While it shares the underlying math with the 'Tangency Tutor', it pivots from education to a high-value regulatory application, filling a gap in demand-side affordability modeling.
Feasibility
5/5
Building an Excel-native calculator based on closed-form algebraic formulas is trivial for a small team.
Wedge clarity
5/5
The wedge is extremely sharp: a specific tool for rate-case affordability hearings that replaces complex econometrics with auditable algebra.
Simplicity / focus
5/5
It avoids 'platform' creep, focusing strictly on a single-purpose calculator for a specific regulatory step.

Scored by Gemma 4 · 12 Oct 2026. Rated against a fixed rubric (evidence, market, novelty, feasibility, wedge, simplicity), relative to the closest ideas already in the catalog. A prior estimate to compare ideas before real-world signal arrives.

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Who benefits

  • Ofwatorganization

    The England and Wales water regulator must weigh bill affordability against cost recovery for financially stressed utilities; a closed-form household demand model gives it a consistent, explainable affordability metric across companies.

  • American Watercompany

    The largest US investor-owned water utility files rate cases across many state commissions; a transparent, auditable model of how proposed rates hit household budgets strengthens its affordability and customer-assistance filings.

  • National Association of State Utility Consumer Advocates (NASUCA)organization

    Member advocates intervene in rate cases with limited analytic budgets; an Excel tool that quantifies rate shock on low-income households from two parameters gives them a defensible exhibit.

  • US EPAorganization

    EPA's Water Infrastructure and Resiliency Finance Center issues affordability guidance tied to household burden; a formula-based demand and crowd-out calculator complements its household-income thresholds.

  • Thames Watercompany

    Facing bill increases under intense affordability scrutiny, it needs to show regulators the household impact of tariff changes; the calculator quantifies crowding-out of other essentials for its customer base.

Research it builds on

  1. Croatian operational research review
    Nataša Erjavec, Ivana Lolić, Petar Sorić · 2026 · 90 citations
    All ideas from this paper →
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