Greywater-to-flush systems for hostels and PGs, paid per kilolitre reused
TL;DR Greywaterly installs and runs small units that clean bath and laundry water from hostels, PGs and budget hotels and send it back for toilet flushing. The owner pays nothing upfront and gets billed per kilolitre reused. I've dropped the seed's plan to pull drinking water out of the air, because the energy cost is far too high.
India's cities produce far more wastewater than they treat. The Central Pollution Control Board estimated urban sewage at 72,368 MLD against an installed treatment capacity of 31,841 MLD, and of 900 plants assessed, only 578 met their consent norms[1]. Meanwhile buildings flush toilets with water bought at drinking-water quality.
Bath and laundry water is the easier part to reuse. A study of Indian households measured average use of 108 litres per person per day, with the heaviest organic load in kitchen water and the most detergent in laundry water[2]. Hostels and PGs, where dozens of people shower and wash clothes in shared bathrooms, produce a steady stream of lighter greywater that goes straight down the drain.
First, the important bit - Greywaterly does on-site treatment of bath and laundry greywater for toilet flushing and garden use only. The water is never supplied for drinking, cooking or bathing, and kitchen and toilet waste stay on the sewer line. Units run under the consent conditions the State Pollution Control Board sets[1].
Greywaterly fits a compact unit in a basement, stilt area or terrace that does screening, settling, filtration and disinfection, with sensors that log volume and basic water quality every hour. A separate flush line carries the treated water to toilet cisterns. Greywaterly owns the unit, services it and bills the owner for metered kilolitres delivered, so the owner only pays when it works.
I reframed the seed, which paired greywater with atmospheric water generation. Research prototypes still use around 3 kWh per litre[3], and a recent review sets under 5 kWh per litre as the target for sorption systems[4]. At that rate a kilolitre needs thousands of units of electricity. Even the best-known Indian startups in this field now sell systems that run on waste heat from data centres and factories[5]. Greywater reuse is the half of the seed that works.
The building owner pays - hostel and PG operators, budget hotels and boarding schools. Residents never see a bill. The price to test is a rate per kilolitre set below what the owner pays for tanker or municipal water today. I found no public benchmark for either in these segments, so this is an assumption. Start with owners who face tanker bills every summer.
AMRUT 2.0, launched on 1 October 2021 with ₹2,99,000 crore, asks states to meet at least 20% of city water demand from recycled water[6]. Its Technology Sub-Mission funds start-up pilots, with projects up to ₹20 lakh approved by a state committee[6]. And the treatment gap in CPCB's inventory means city sewers won't close this anytime soon[1].
Nobody publishes a figure for greywater reuse in Indian buildings. The narrowest anchor is policy, a 20% recycled-water target per city under AMRUT 2.0[6]. There's one public example - Surat started tertiary treatment of sewage for toilet flushing and gardening in an EWS housing scheme of more than 3,000 units[1]. The 72,368 MLD of urban sewage[1] is context, not your market.
One Bengaluru startup began in atmospheric water and now pitches waste-heat cooling with distilled water as a by-product, up to 30,000 litres per MW per day[5]. Surat Municipal Corporation reuses treated water for flushing in public housing, a model for what cities may require[1]. Beyond these, the default is a full sewage treatment plant built by a local contractor and run by the building.
I found no Indian company publicly offering greywater reuse to hostels or PGs on a pay-per-kilolitre basis.
| Difficulty | Moderate (50/100) |
| Starting capital | ₹1.1–2.1 Cr |
| Time to launch | 8–12 months |
The treatment technology is known. The hard parts are plumbing and upkeep. Older buildings mix all wastewater in one pipe, and adding a separate flush line can cost more than the unit. Untreated greywater turns foul quickly, so a missed service visit becomes a smell complaint within days. And owning the assets means carrying capital at every site.
Yes, this one touches environmental and building rules, so sort out approvals before your first install.
Building this outside India? The categories above usually have a local equivalent, so check with your own regulator.
Don't trust AI to declare water safe. Treated greywater still needs disinfection and lab testing, and a sensor reading isn't a health clearance.
Want to work out the AI layer for Greywaterly? Talk to Yash →
Here's what can go south -
I'd back this for a founder with water-treatment or plumbing-contracting experience who's comfortable owning hardware in the field. It's a poor fit if you're hoping for a light software business.
Before raising money, run three sites for one summer and show that each reuses enough kilolitres to cover its own servicing.
Plan for roughly ₹1.1–2.1 Cr, because you pay for the units upfront and recover the cost per kilolitre reused. That's the price of offering owners zero upfront cost.
Likely yes. Check State Pollution Control Board consent for treatment units and local plumbing approval for flush lines, on top of company and GST registration.
Yes, the model fits any city with water stress and shared housing. Greywater reuse rules differ widely, so check with your local regulator first.
The free Greywaterly validation kit has the line-by-line capital breakdown, the effort scoring, the pollution-control and plumbing checklist, a 14-day validation sprint with pass/fail targets, a 90-day launch plan, 10 interview questions for building owners, and 5 assumptions to test. Download the kit →
Thinking about building Greywaterly or something close to it? The make-or-break work is pricing per kilolitre so that each site pays for its own retrofit and servicing, and that's the kind of maths I help founders work through. If you need a hand, you know where to find me. Talk to Yash →
For illustration only. Names are fictional and ideas hypothetical; sourced facts are real but may be out of date. Nothing here is legal, financial or professional advice, and Yash Khatri is not personally liable for any use of it. Read the full disclaimer.