Interactive Calculator · 2026
STP ROI & Payback Calculator
See how fast a sewage treatment plant pays for itself. Enter the capex, how much treated water you reuse and what fresh water costs — get the payback period, net annual savings and return on investment.
Annual water-reuse savings vs annual operating cost
Your STP economics
One-time capex to build and commission the plant.
Treated water actually reused per day, kilolitres.
Price of the fresh/tanker water each reused kilolitre replaces.
Power, chemicals, labour and maintenance per year.
Where the money comes from
Annual water-reuse savings against the plant's annual running cost — the gap is your net gain.
Reusing 160 KLD of treated water replaces 58,400 KL of bought water a year, worth ₹35,04,000.
After the ₹7,00,000 running cost you net ₹28,04,000 a year — the capex is recovered in about 0.9 years.
How this is calculated
- Water reused / year = reuse KLD × 365 = 160 × 365 = 58,400 KL.
- Annual savings = water reused × ₹/KL = 58,400 × ₹60 = ₹35,04,000.
- Net annual savings = annual savings − operating cost = ₹35,04,000 − ₹7,00,000 = ₹28,04,000.
- Payback = capex ÷ net annual savings = ₹25,00,000 ÷ ₹28,04,000 = 0.9 years.
- ROI = net annual savings ÷ capex = 112.2% per year.
A concept-level cash view of reuse economics only. Real appraisals also weigh discharge-compliance savings, tariff escalation, financing and the cost of the water you'd otherwise buy — confirm with a qualified consultant.
Related Guides — Deep-dive reading
ROI of Water Recycling: Does an STP Actually Pay for Itself?
A numerate, honest look at the payback case for on-site sewage treatment in India — what a recycled kilolitre is really worth, what the plant costs to build and run, and how many years it takes to break even.
Sewage Treatment PlantsMBR STP Cost Guide: What a Membrane Bioreactor Really Costs in India (2026)
Why MBR carries the highest capital and running cost of any sewage treatment technology in India — membranes, power and replacements — and exactly when that premium pays for itself through water reuse and a smaller footprint.
Sewage Treatment PlantsReducing an STP's Carbon Footprint: The Net-Emissions Guide
An STP burns power around the clock — but the treated water it produces displaces tankered and pumped freshwater. This guide shows how to weigh the two, then shrink the net carbon footprint with efficient aeration, solar and biogas.
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