Can laboratory chemicals go down the drain?

The law on chemicals in sewers and drains

In England and Wales, two provisions of the Water Industry Act 1991 do most of the work.

Section 111 makes it an offence to put certain things into a public sewer, or into a drain leading to one. These include anything likely to injure the sewer or interfere with the treatment of its contents. They also include petroleum spirit, and chemical refuse that is dangerous, a nuisance or injurious to health, alone or in combination with what is already in the sewer.

Section 118 deals with trade effluent. Liquid from trade premises can go to a public sewer only with the sewerage undertaker's consent, and the occupier commits an offence if it is discharged without one.

Government's pollution prevention guidance puts the same idea in simple terms. Polluting liquids can go to the foul drain only with permission from your water company. Otherwise a registered waste carrier removes them. Surface water drains discharge directly to the environment, so they should only ever take clean water.

Scotland and Northern Ireland have their own sewerage legislation and their own water authorities. Expect the same principle there, and ask locally about the detail.

For hospitals, HTM 07-01 gives its own steer: care should be taken to ensure liquid chemical wastes are never disposed of down the drain.

Do you know where your lab's sink actually goes?

Most lab staff have never seen a drain plan, and it matters. An older school building may have a misconnection, sending a sink's water to a surface water drain. Government guidance recommends a drain plan showing where drains run and which type each one is. Your premises team may have one.

Older science blocks can also have glass or lead pipework and catch pots that have been collecting residues for decades. What went down a sink in 1975 may still be there. That is a reason to tell any contractor about the history of the room before they open a trap.

Five arguments you may hear, and why they fall short

"It is only a small amount." Section 111 does not set a minimum, and small amounts are how long-term contamination builds. Think also of the pattern. One bottle from one lab, repeated across a department every week of term, is not a small amount. Phenol illustrates the point: it is toxic, it is absorbed through skin, and it is the sort of chemical whose effect on a treatment works is a real concern.

"We have diluted it." Diluting a waste does not change what it is, and it adds water to something that must still be dealt with. If you need a technical reason, consider the receiving works, where the total load matters and not the strength from your sink. Dilution is also an extra handling step, which adds exposure.

"We have neutralised it." Neutralising an acid or an alkali requires a controlled process, a risk assessment and knowledge of what the resulting salts are. Doing it to avoid a disposal bill can amount to treating waste, and it can produce a hot or violent reaction in unskilled hands. We publish no method for it, and we advise against it in a clear-out.

"It evaporates, so it never reaches the sewer." Solvents such as chloroform do evaporate, and the vapour then enters the room and the pipework. Chloroform is toxic if inhaled and suspected of causing cancer. A warm lab with a shared drain can draw vapour back to other rooms through dry traps. Flammable vapours in a drain can also create a fire risk. Evaporation in a fume cupboard is not a disposal route either.

"The old technician always did it this way." Older practice varied widely, and it is no defence. The 1970s teaching lab was not a good model for much of what it did with chemicals.

Where school practical waste fits in

School technicians will know the awkward middle ground. Some class practicals produce small volumes of dilute, low-hazard aqueous waste, and your advisory service may address how those are handled for specific activities. If you are a member of CLEAPSS, or SSERC in Scotland, follow what they say for that activity and record it in your risk assessment.

The dividing line is simple. Check what your own assessment says for each activity, and do not stretch it to fit a stock clear-out. Advice written about the washings from a class experiment does not stretch to a Winchester of old solvent found at the back of a cupboard. Where your assessment is silent, collect it.

What to do with lab waste instead

Collect waste in a sound container that is compatible with its contents, label it with what went in, and keep incompatible streams apart. Never add to a waste bottle without knowing what is already in it. Solvent waste bottles deserve particular care, since an oxidising acid added by mistake can build pressure or start a fire. Do not fill them to the brim. Keep the lid closed.

Classify the waste, hold it securely and pass it to an authorised business. Regular streams, such as histology xylene or chlorinated solvent from a research lab, are usually best on a regular schedule, so nobody is tempted by a full bottle on a Friday.

Unstable or unidentified material is different. Do not pour it, dilute it or decant it. Leave it in place and get a specialist assessment.

If something has already gone down the drain

Do not try to flush it through with lots of water. If there is any danger to people, such as fumes, fire or an injury, get people out and call 999. Follow your COSHH emergency procedure and tell your manager.

Then report it. Your water company needs to know if chemical waste has reached a foul sewer, and needs to know what it was and roughly how much. If it may have reached a surface drain, a stream or the ground, in England call the Environment Agency incident hotline on 0800 80 70 60. Wales, Scotland and Northern Ireland have their own reporting routes, shown on that page. Early reports let others protect the works and the watercourse.

For the regular streams, our solvent waste collection page explains how labs keep a scheduled route in place, so the sink never looks like the easy option.