--- title: "Wattey — Fair electricity sub-billing" headline: "Wattey — Electricity Sub-Billing for Multi-Tenant Buildings" description: "Ali Ahmed built Wattey Sub-Billing: fair per-resident electricity billing for buildings on one bulk meter — measured from real readings and the exact time present, even as people move in and out." canonical_url: https://alioahmed.com/work/electricity-sub-billing type: case-study role: "Head of Energy Systems & Product Engineering, BijliBachao.pk" date_label: "2026 · entering production" status: pre-launch date_modified: 2026-09-22 author: name: "Ali Ahmed" url: https://alioahmed.com/ orcid: https://orcid.org/0009-0007-4265-3295 key_figures: - "265 beds · ~160 sub-meters, billed as one fair bill each" - "To the paisa books reconcile across mid-month move-ins and move-outs" - "Measured not estimated — from real readings and real time present" entities: - name: "Wattey Sub-Billing" type: SoftwareApplication - name: "BijliBachao.pk" type: Organization url: https://www.bijlibachao.pk/ same_as: - https://bijlibachao.pk/#organization person_same_as: - https://www.linkedin.com/in/alioahmed/ - https://github.com/alioahmed - https://orcid.org/0009-0007-4265-3295 - https://x.com/Alioahmed_ - https://about.me/alioahmed - https://dev.to/alioahmed - https://medium.com/@alioahmed - https://hashnode.com/@alioahmed - https://substack.com/@alioahmed - https://huggingface.co/alioahmed - https://bsky.app/profile/alioahmed.bsky.social - https://mastodon.social/@alioahmed - https://www.kaggle.com/alioahmed - https://www.producthunt.com/@alioahmed - https://www.patreon.com/cw/alioahmed - https://www.goodreads.com/user/show/202106301-ali-ahmed - https://fueler.io/alioahmed - https://gitlab.com/alioahmed - https://linktr.ee/alioahmed - https://topmate.io/alioahmed related: - https://alioahmed.com/work/tenantbill - https://alioahmed.com/work/wattey - https://alioahmed.com/work/bijli-bachao full_corpus: https://alioahmed.com/llms-full.txt site_index: https://alioahmed.com/llms.txt --- # Wattey — Fair electricity sub-billing > Wattey Sub-Billing is a fair electricity sub-billing platform built by Ali Ahmed at BijliBachao.pk. When a building buys power in bulk and re-bills the people living inside it, it divides that one shared bill into per-resident bills measured from actual meter movement and the exact time each person was present — not a RUBS-style estimate. It solves the part operators get wrong (people moving in and out mid-cycle): it settles a leaver on the day they walk out, backs every reading with a photograph, reconciles the month to the last paisa, and locks the money records so they cannot be quietly altered. Built and independently stress-tested for correctness and security against a real 265-bed residential property before it billed a single rupee — built, verified, and entering production for its first building. **Canonical URL:** https://alioahmed.com/work/electricity-sub-billing **Role:** Head of Energy Systems & Product Engineering, BijliBachao.pk — 2026 · entering production **Summary:** Ali Ahmed built Wattey Sub-Billing: fair per-resident electricity billing for buildings on one bulk meter — measured from real readings and the exact time present, even as people move in and out. ## Key figures - **265 beds** — · ~160 sub-meters, billed as one fair bill each - **To the paisa** — books reconcile across mid-month move-ins and move-outs - **Measured** — not estimated — from real readings and real time present ### What Ali built. Ali Ahmed builds production systems where the numbers have to be exactly right and defensible. Wattey Sub-Billing is one of them: a fair electricity sub-billing platform for buildings that buy power in bulk on one connection and re-bill the many people living inside — hostels, student housing, co-living, serviced apartments and short-lets. It divides that one shared utility bill into a fair, itemised, evidence-backed bill for every resident — measuring what each person actually used, for the exact time they were there, from real meter readings with a photograph behind every one. It was built for Bijli Bachao and deployed for a 265-bed residential property in Lahore, Pakistan, across 94 rooms and ~160 sub-meters. It is built, independently stress-tested, and entering production for its first building — not yet a multi-building platform with live payment volume. ### The bill is easy. The people are the hard part. A building pays the utility one large bill each month and has to recover that money fairly from everyone inside. That would be simple if everyone stayed all month. They do not: someone moves in on the 12th and should not pay for the first 11 days; someone leaves on the 20th and needs their final bill that day; one room has three different occupants across the month; and at term start half the building can turn over in a week. Operators handle this two ways, and both break. Spreadsheets are slow, error-prone, and impossible to defend when a figure is disputed. Estimates — dividing the bill by room size or headcount (RUBS) — are faster but a guess: the resident who was away all month pays like the one who ran the AC every night, and nobody can prove the number is fair, because nothing was measured. ### Measured, not estimated — what it does. Wattey Sub-Billing divides the bill the only way that is actually fair: by what each person used and how long they were there, from real readings, with evidence behind every number. - Fair to the day — each resident’s bill starts the day they move in and ends the day they leave. Present nine days, billed nine days. - Backed by evidence — every reading is captured with a photo of the meter, filed against the resident it concerns. Disputes are settled by the picture, not by argument. - Settled on the day they leave — a mover-out’s exact final bill is ready immediately, so dues clear at the door. - The books always balance — everything billed across the month, leavers and stayers alike, adds up to exactly what the building consumed. To the paisa. - Reconciled to the utility bill — each month, what was billed out versus what the utility charged, clearly. - Records you can defend — once bills and payments are made, the figures are locked. Corrections happen on the record, with a trail — never a silent edit. ### Where the real work went. Anyone can divide a number by a headcount. The difficulty — and where Ali spent the engineering — is getting it right under real-world mess and proving it. The month divides at each meter reading, and each segment is shared only among who was actually present in it, so a mid-month arrival never pays for electricity burned before they showed up. Each person’s reading is captured and filed against their name with a photograph, turning “trust me” into “look at the meter.” Rooms with two meters, one, or none, and commercial units on their own rate, are all handled rather than assumed away — and when a shared amount cannot divide evenly to the last unit, the leftover is rotated rather than always landing on the same person. The books provably close: interim bills for leavers plus month-end bills for the rest sum to exactly what the building consumed, checked by an automated proof suite — 300+ automated database and security proofs and 70+ billing test cases — that walks a full month of arrivals, departures, payments and reversals every time. The money ledger is tamper-evident — a reversal is recorded, not erased. And the whole platform was engineered and independently stress-tested for correctness and security — from the position of an outsider and of a low-privilege staff member — before it handled a single real bill, so a resident’s private data cannot leak and the money records cannot be tampered with. ### Built for a real building, not a demo. The system was built for, and verified against, a genuine multi-tenant property: 7 floors, 94 rooms, 265 beds, and roughly 160 electricity sub-meters — of several kinds, including shared rooms, self-contained apartments, offices and common areas that are metered but never billed to a resident, and a commercial unit on its own rate. Most rooms have two meters, some have one, a few have none, and the system handles each case correctly rather than assuming one meter per unit. It is two surfaces, one system: a management dashboard for the office — rooms, residents, readings, bills, collection and the monthly reconciliation — and a field app for the person who walks the building, photographing each meter and reading the number, working offline and syncing when back in range. A reading taken in the corridor becomes a line on a bill in the office, with its photograph attached, without anyone re-typing anything. ### One connection, many changing residents — who else has this problem. The pattern repeats anywhere a single bulk electricity connection serves many people who come and go — which is the market beyond hostels: - Hostels and guest houses - Student housing and purpose-built student accommodation (PBSA) - Co-living spaces - Serviced apartments - Short-let and Airbnb portfolios - Apartment blocks on a master meter - Worker accommodation - Mixed-use buildings with shops on a shared supply ### Where it stands. Wattey Sub-Billing is built, rigorously verified, and entering production for its first building. The management dashboard runs end to end against a real database; the field app captures readings with photo evidence, offline queueing and automatic meter-reading recognition; and the billing engine is proven to balance across a full month of turnover before it touches real money. The strongest true claim is depth and correctness on a real 265-bed property — not scale of usage, which is honestly still ahead. ## FAQ ### How is this different from dividing the bill by number of occupants? That is an estimate. Wattey Sub-Billing measures each person’s actual share from real meter readings and the exact time they were present — not a RUBS-style formula based on room size or headcount. The resident who was away all month does not pay like the one who ran the AC every night. ### What happens when someone moves in or out mid-month? Their bill starts or ends on the exact day. A leaver’s final bill is ready the day they go, with the meter reading of that day behind it, so dues clear at the door rather than waiting for month end. Everything billed across the month still reconciles to exactly what the building consumed. ### What if a resident disputes their bill? Every reading has a photograph of the meter, filed against that resident, and the bill shows its own working — the days present, the readings behind it, and the photographs. Disputes are settled by evidence, not argument. ### Does it work if a room has more than one meter? Yes. Each meter is read on its own and the room’s real consumption is combined correctly. Rooms with two meters, one, or none, and commercial units on their own rate, are all handled rather than assumed away. ### What kinds of buildings is it for? Any building on one bulk electricity connection with residents who come and go — hostels, student housing and PBSA, co-living, serviced apartments, short-let and Airbnb portfolios, apartment blocks on a master meter, and worker accommodation. ### Is it live yet? It is built, independently stress-tested for correctness and security, and entering production for its first building — a 265-bed residential property in Lahore. The dashboard and field app run end to end; the billing engine is proven to balance across a full month of turnover before it handles real money. It is not yet a multi-building platform with live payment volume. --- Rendered from the structured content at https://alioahmed.com/work/electricity-sub-billing. Facts trace to the canonical bio; render, don't reword.