Water Savings & Utility Cost Impact
Updated February 20, 2026
Toilets are the biggest water user in most homes -- about 30% of indoor water consumption. An old 3.5 GPF toilet uses more than twice the water of a modern 1.28 GPF model. For a family of four, that difference adds up to 15,000+ gallons per year. At current water rates, upgrading pays for itself faster than most people expect.
Overview
Toilets are the biggest water user in most homes -- about 30% of indoor water consumption. An old 3.5 GPF toilet uses more than twice the water of a modern 1.28 GPF model. For a family of four, that difference adds up to 15,000+ gallons per year. At current water rates, upgrading pays for itself faster than most people expect.
Cost Breakdown
Pro Tips
- Replace the highest-use toilet first (usually the primary bathroom) for the fastest payback.
- WaterSense certification guarantees the toilet flushes well at 1.28 GPF or less. Don't worry about weak flushes -- modern designs are far better than early low-flow models.
- If your home has 3+ toilets, replacing all of them at once often qualifies for larger rebates and plumbers may offer a multi-toilet discount.
- Track your water bill before and after replacement. The savings are real and visible within one billing cycle.
Mistakes to Avoid
- Assuming low-flow means weak flush. WaterSense toilets are independently tested for flush performance.
- Not checking for local rebates before purchasing. Some rebates require pre-approval or specific models.
- Replacing only 1 of 3 toilets and expecting dramatic savings. All toilets need to be efficient for full impact.
- Ignoring the sewer portion of the water bill. You pay for water going in AND water going out -- efficient toilets reduce both charges.
When to Call a Pro
If you're replacing multiple toilets, a plumber can often do all of them in a single visit for less per-toilet than individual visits. If you want to maximize rebate value, some utilities partner with specific plumbers who handle the paperwork.
Bottom Line
Replacing a 3.5 GPF toilet with a 1.28 GPF model saves a family of four $200-$400 per year on water and sewer bills. The toilet pays for itself in 1-3 years. After that, it's pure savings for the next 15-20 years.