{
  "slug": "water-fixture-retrofit-savings",
  "title": "Water Fixture Retrofit Savings Calculator",
  "heading": "Low-Flow Fixture Retrofit Savings Calculator",
  "category": "financial",
  "url": "https://www.revenuelab.fyi/toolbox/water-fixture-retrofit-savings",
  "summary": "Water and cost savings from switching to low-flow toilets, faucets, and showerheads.",
  "description": "Retrofitting older fixtures with WaterSense-certified low-flow toilets, faucets, and showerheads is one of the fastest-payback water conservation investments available, often paying back in under two years in commercial buildings with moderate to heavy restroom traffic. This calculator compares your current fixture flow rates against low-flow replacements, factoring in daily uses per fixture and combined water plus sewer cost (sewer rates are often based on metered water use even though the water doesn't return to the sewer system, which is a detail that inflates real-world savings beyond the water cost alone). It's the standard calculation behind LEED water-efficiency credit applications and behind most municipal water utility rebate program qualification worksheets, which typically require documented baseline and post-retrofit flow rates.",
  "formula": "Annual gallons saved = uses/day × (old gal/use − new gal/use) × fixture count × 365. Savings = gallons saved ÷ 1000 × combined water+sewer rate.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=water-fixture-retrofit-savings",
  "inputs": [
    {
      "id": "toilets",
      "label": "Number of toilets to retrofit",
      "kind": "number",
      "hint": null,
      "default": 30,
      "unit": null,
      "min": 0,
      "max": null
    },
    {
      "id": "oldGpf",
      "label": "Current toilet flush volume",
      "kind": "number",
      "hint": null,
      "default": 3.5,
      "unit": "gal/flush",
      "min": 0.5,
      "max": null
    },
    {
      "id": "newGpf",
      "label": "Low-flow toilet flush volume",
      "kind": "number",
      "hint": null,
      "default": 1.28,
      "unit": "gal/flush",
      "min": 0.5,
      "max": null
    },
    {
      "id": "usesPerDay",
      "label": "Uses per fixture per day",
      "kind": "number",
      "hint": null,
      "default": 8,
      "unit": null,
      "min": 0,
      "max": null
    },
    {
      "id": "waterRate",
      "label": "Combined water + sewer rate",
      "kind": "number",
      "hint": null,
      "default": 9.5,
      "unit": "$/1,000 gal",
      "min": 0,
      "max": null
    },
    {
      "id": "retrofitCost",
      "label": "Installed cost per toilet",
      "kind": "number",
      "hint": null,
      "default": 280,
      "unit": "$",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "annualSavings",
      "label": "Annual cost savings",
      "format": "currency",
      "hint": null,
      "primary": true
    },
    {
      "id": "annualGallons",
      "label": "Annual gallons saved",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "totalCost",
      "label": "Total retrofit cost",
      "format": "currency",
      "hint": null,
      "primary": false
    },
    {
      "id": "paybackYears",
      "label": "Payback period",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Number of toilets to retrofit: 30",
      "Current toilet flush volume: 3.5 gal/flush",
      "Low-flow toilet flush volume: 1.28 gal/flush",
      "Uses per fixture per day: 8",
      "Combined water + sewer rate: 9.5 $/1,000 gal",
      "Installed cost per toilet: 280 $"
    ],
    "outputs": [
      "Annual cost savings: $1,847",
      "Annual gallons saved: 194,472",
      "Total retrofit cost: $8,400",
      "Payback period: 4.55"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter number of toilets to retrofit.",
      "Enter current toilet flush volume (gal/flush).",
      "Enter low-flow toilet flush volume (gal/flush).",
      "Enter uses per fixture per day.",
      "Enter combined water + sewer rate ($/1,000 gal).",
      "Enter installed cost per toilet ($).",
      "Read your annual cost savings on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "toilets": 18,
        "oldGpf": 2.1,
        "newGpf": 0.768,
        "usesPerDay": 5,
        "waterRate": 5.7,
        "retrofitCost": 170
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "toilets": 30,
        "oldGpf": 3.5,
        "newGpf": 1.28,
        "usesPerDay": 8,
        "waterRate": 9.5,
        "retrofitCost": 280
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "toilets": 48,
        "oldGpf": 5.6000000000000005,
        "newGpf": 2.048,
        "usesPerDay": 13,
        "waterRate": 15.200000000000001,
        "retrofitCost": 450
      }
    }
  ],
  "limitations": [
    "Results are estimates before tax, fees, and inflation unless an input explicitly covers them.",
    "Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.",
    "This is educational maths, not financial advice. Check anything contractual with the lender or your accountant."
  ],
  "faq": [
    {
      "q": "Why does sewer cost matter here if the water doesn't go into the sewer differently?",
      "a": "Most utilities bill sewer charges based on metered water consumption as a proxy for wastewater volume, regardless of where the water actually ends up, so cutting water use cuts your sewer bill proportionally too. That combined rate is why fixture retrofits often show better paybacks than a water-only rate calculation would suggest."
    },
    {
      "q": "Are there rebates for low-flow fixture retrofits?",
      "a": "Many water utilities, especially in drought-prone regions of the Southwest and California, offer per-fixture rebates for WaterSense-certified toilet and faucet replacements, sometimes $50-200 per toilet. Check your local water utility's conservation program before budgeting the full retrofit cost out of pocket."
    },
    {
      "q": "Do low-flow toilets actually work as well as older high-flow models?",
      "a": "Early-generation low-flow toilets (mid-1990s to early 2000s) had a real reputation for clogging and requiring double-flushing, but current WaterSense-certified models (1.28 gpf or less) use improved bowl geometry and trapway design that perform comparably to older 3.5-gallon models in independent flush-performance testing (like the Maximum Performance Testing program)."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/water-use-intensity",
    "https://www.revenuelab.fyi/toolbox/led-retrofit-payback",
    "https://www.revenuelab.fyi/toolbox/building-eui"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Water Fixture Retrofit Savings Calculator (https://www.revenuelab.fyi/toolbox/water-fixture-retrofit-savings)"
}