The RO had been leaking a thin stream all night, and at 5:30am the plastic drum under the kitchen sink was a lake on the floor. The motor in the courtyard was still trying to fill the overhead that had already overflowed once this week. Reject water has to go somewhere. In a Gurgaon builder floor or a Jaipur row house, “somewhere” is often a drum that nobody emptied, a drain that silted, or a pipe a well-meaning uncle tied back into the underground tank to “save water.” That last trick fills the tank with brine and then dumps it on the tiles.
A domestic RO throws out more water than it keeps, especially on hard North Indian and Rajasthan supply. That reject is salty and must leave the drinking cycle. If it cannot reach a drain, it becomes overflow. If it reaches the underground tank, it becomes a slow poisoning of the very water the motor lifts. Fix the path of the waste first. Then talk about TDS.
Home checks under the sink and at the tank
Follow the reject pipe with your hand. It should end in a drain, a dedicated waste drum you empty, or a garden use that can take salt, not into the drinking underground. If you find a tee that joins reject to the tank inlet, break that idea. Saving reject into the same tank the RO drinks from is a loop. The TDS climbs. The RO works harder. The drum still overflows because the whole house water got worse.
See whether the drain is blocked. Kitchen nali silt, a plastic bag, and a RO that ran all night are a famous trio. Clear the nali. Do not pour acid as a weekly religion.
Check the tank that overflowed. Is it the reject drum, the underground, or the overhead? Three different faults. Drum: empty it on a schedule or plumb to drain. Underground: ball cock, plus any reject tee. Overhead: float, plus the motor hours, plus whether reject is somehow being pumped up.
Feel the RO. A unit that never stops because the tank float in the purified storage is stuck will waste all night. That is an RO service, not a bigger drum.
If you use reject for mopping, use a drum with a tap, and do not let it sit until it smells. Salt water on a marble floor also leaves a white crust. That is a house choice, not a flood.
Photos to take for the RO mechanic
Photograph the reject hose end. Photograph the illegal tee into the tank if it exists. Photograph the overflow on the floor with the time. Photograph the RO model sticker and the last service card. Photograph the drain mouth.
A mechanic who did not see the tee will only change a membrane and leave. The overflow will return.
If the overflow damaged a downstairs neighbour, photograph your stop: RO unplugged, motor off. Same habit as a tank overflow. Source first.
Neighbour timing on shared drains and shared motors
In a builder floor the kitchen drain is a stack. Your RO reject at 5:30am plus their washing machine can blow a joint on the second floor. If the leak is in the shaft, it is a society plumber plus your reject volume. Reducing night-time RO running helps the stack. A auto-flush that runs at dawn on three floors is a planned flood.
If you share an underground tank, one house tying reject back in ruins the TDS for everyone. Show them the hose. A shared tank needs a shared no.
A neighbour who wants your reject for their plants can take a drum, not a live pipe across a wet balcony. Live pipes trip people at 5:30am.
Complaint and repair path
Unplug the RO if it is flooding. Clear the drain. Reroute the reject to a legal waste point. Call the RO service for a stuck auto-start, a failed purified-tank float, or a membrane that is dumping because it is dead. A dead membrane can change the waste ratio and the smell.
If someone tied reject into the drinking tank, drain that tank and rinse before you drink. Then test if the family is uneasy. The RO prefilter will also have suffered if the feed TDS spiked.
Society complaint if the stack leaked. House plumber if the nali is yours. RO company if the machine never shut off.
Do not “fix” overflow by pointing the reject hose out of the window onto the gali. That is how a slippery road and a fine start. Do not point it into a storm drain that backs up into the kitchen.
Municipal line complaints are separate. Low pressure makes people run the RO longer on a booster, which makes more reject. Fixing pressure is the jal board. Fixing the hose is you.
If a technician offers to reduce waste by a secret bypass that also reduces purification, ask what that does to the water you drink. A honest setting is a service. A cheat that puts half-filtered water in the glass is not a saving.
Approximate INR rates that vary by ward
An RO service visit in many North Indian wards is Rs 300 to Rs 900, sometimes free if a AMC is alive. A float or auto-start part may be Rs 200 to Rs 1,200. A membrane replacement is a wide band, often Rs 1,200 to Rs 4,500 depending on brand and who is selling. Re-plumbing a reject line to a proper drain can be Rs 250 to Rs 1,500 in PVC and labour. A larger waste drum with a tap is often Rs 200 to Rs 800. Cleaning a blocked kitchen nali may be Rs 200 to Rs 1,000, more if they must open a floor trap. If reject in the underground tank forces a clean and two tanker flushes, add the cleaner and tanker lines you already know from tank work, which can exceed Rs 2,000 easily. Builder-floor plumbers charge more for shaft work, Rs 1,000 to Rs 5,000 when they must coordinate two houses. Ward AMC rates printed on your RO card beat a flyer from another sector. Get the spare name on the bill.
A “free waste reducer” sold on the pavement is often a gadget that hurts drinking quality. Pay for a drain, not a miracle.
FAQ
Can I put RO reject back into the underground tank to save motor units?
You save a little water on paper and spend it on worse TDS, a harder RO, and a tank that smells of salt. The motor then runs more, not less. Put reject in a drain or in a mop drum. Do not feed the drinking tank.
Why did the drum overflow only in summer?
You run the RO more because the municipal TDS and the heat both rise, and guests drink more. The waste ratio was always there. Summer only makes the drum honest. Plumb it or empty it daily.
The RO man says waste is normal. Is overflow normal?
Waste is normal. Overflow on the floor is a plumbing failure or a machine that never stopped. Normal reject still needs a path that does not flood the kitchen.
Will a bigger RO stop the overflow?
A bigger unit can throw more waste if you still have no drain. Fix the hose and the auto-off. Size is a later shop question after the floor is dry.
Short note
Paani Atka is not a jal board and not an RO company. The official water office is final for supply and pressure. Your kitchen hose is your house. If overflow and hard water push someone to sell you a new boring as the only way out, that boring needs a local permit. Do not drill to hide a reject pipe, and do not tie waste into the drinking tank.