The Munimetric Infrastructure Stress Index (MISI) is a deterministic, source-backed measure of structural stress across U.S. community drinking-water service markets. MISI aggregates five bounded scoring families into a 0–100 headline composite while preserving provenance, as-of dating, mapping confidence, score confidence, and versioned methodology logic. Version 0.1.2 keeps the same five-family headline structure and signal-type decomposition introduced in v0.1.1. This release adds frozen-reference variance weighting and a 50 percent single-factor concentration guardrail to reduce saturated-factor dominance in comparative rankings. MISI remains a blended structural stress composite spanning operational burden, capital pressure, revenue fragility, rate constraint, and governance risk. It is not a pure physical infrastructure-condition index and does not constitute investment advice, a credit rating, municipal advisory services, or a recommendation to buy, sell, or hold any security. Project website: https://munimetric.com