Industrial plumbing: the water in, the waste out, and who is responsible for both

01 What makes plumbing industrial

A house takes in drinking water and sends out sewage, and both are well understood quantities. A factory, workshop, laundry, food plant or treatment works does something harder: it takes water in, changes it (heats it, pressurises it, mixes chemicals or product into it, runs it through machines), and then has to get rid of whatever it has become. Four things change once you cross that line, and every section below follows from them.

The water is put to work, not just used. Process water might be softened, filtered, chilled, boiled or dosed before a machine will accept it, and it leaves carrying heat, solids, fats, metals or chemicals it did not arrive with.

The duty is continuous. A domestic pipe sees a few minutes of flow an hour. An industrial line can run at temperature and pressure all shift, every shift, and materials that shrug off intermittent use fatigue and corrode under constant load.

The effluent is not ordinary sewage. Anything other than normal domestic wastewater is trade waste, and you cannot simply put it down the sewer. It has to be pre-treated to an agreed standard and discharged under an agreement with your water authority (section 05).

The compliance load sits with the occupier. A plumber installs and certifies the pipework, but the ongoing obligations, the trade-waste agreement, the backflow test records, the cooling-tower register, the environment licence, belong to the business that runs the site. Not knowing that is the single most expensive mistake in this guide.

02 The water coming in

Every industrial site draws from the same town main as the houses around it, and the water authority has one non-negotiable concern about that connection: nothing that happens on your site can ever get back into the public supply. That risk is real on industrial sites in a way it never is at home.

Backflow, and why it is taken so seriously. If pressure in the main drops (a burst nearby, heavy draw at a hydrant), water can be pulled backwards through your pipework. On a site where the pipework connects to chemical dosing tanks, process vessels, cooling systems or a wash bay, that back-siphoned water can carry contaminants straight into the drinking supply. The defence is a testable backflow prevention device sized to the hazard, installed at the boundary. On medium and high-hazard connections it must be tested by an accredited person and the result recorded, typically every year. That test record is the site's to keep, not the plumber's.

Treating the water for the process. Raw town water is fine for drinking and rarely fine for a machine. Depending on the process it may need:

• Filtration to strip suspended solids, from a coarse self-cleaning strainer down to fine media filters.
• Softening or dealkalisation to pull out the calcium and magnesium that scale up boilers, heat exchangers and membranes.
• Membrane treatment where the process needs genuinely pure water: ultrafiltration for fine particles and microbes, then reverse osmosis for dissolved salts, run in sequence so the coarse stages protect the expensive one.

The rule of thumb that saves the most money is simple: put the cheap, robust treatment first so the fragile, expensive treatment lasts. An RO membrane fed unfiltered water fouls in weeks.

03 Pressure, heat and the pipes

Industrial lines carry more energy than domestic ones, and that energy is what eventually finds any weakness in the system. Three forces do most of the damage.

Pressure. Higher working pressures mean thicker pipe walls, rated fittings and, on genuine high-pressure or pressure-vessel systems, equipment that falls under separate pressure-equipment rules rather than ordinary plumbing. Pressure is also not constant: a pump starting, a valve slamming shut, or a process cycling can spike the line well above its steady figure.

Water hammer, scaled up. When fast-moving water is stopped suddenly by a quick-closing valve, its momentum has nowhere to go and slams through the pipework as a pressure wave. In a house that is an annoying bang. On an industrial line carrying more mass at more speed, the same wave cracks fittings, splits gauges and fatigues joints. It is managed with slow-closing valves, air chambers or arrestors, and proper pipe support, not by hoping the pipe holds.

Temperature. Hot process lines expand, and a long steel run can grow by a surprising amount between cold and working temperature. Held rigid, that movement tears at anchors and joints; the fix is expansion loops and sliding supports designed in from the start. Heat also drives corrosion and lowers the pressure a material can safely hold, so a line that is fine cold can be marginal hot.

04 Corrosion, the slow failure that sets your budget

Most industrial pipe does not fail in a dramatic burst. It corrodes, quietly, from the inside, and the first you know of it is a weep, a pressure drop or a stain. Knowing which mechanism you have is what turns replacement from a surprise into a plan.

Galvanic corrosion. Join two dissimilar metals (copper to steel, for instance) in the presence of water and you have made a battery. The less noble metal corrodes preferentially at the junction. It is why material transitions need the right dielectric fittings, and why a well-meant repair in the wrong metal can eat a joint within a season.

Pitting and crevice corrosion. Localised attack that drills narrow holes rather than thinning the whole wall. It hides under deposits and in stagnant crevices, and a pipe can look sound from outside while a pit has almost breached it.

Erosion-corrosion. Fast or turbulent flow, especially with any grit in it, strips the protective film off the metal and lets corrosion restart continuously. It shows up at elbows, valves and anywhere the flow changes direction.

Microbially influenced corrosion. Bacteria in low-flow or stagnant water form colonies that corrode the metal beneath them. Dead legs and rarely-used lines are the classic sites.

The water itself sets the pace. Low pH, high temperature, dissolved oxygen and chlorides all accelerate the reactions, which is why the treatment choices in section 02 are also corrosion decisions. Where corrosion cannot be designed out, it is managed: correct material selection, protective linings and coatings, cathodic protection on buried and immersed metalwork, and regular wall-thickness checks so a line is replaced on evidence rather than after a failure.

05 The waste going out

This is the section that catches sites out, so it is worth stating plainly: the sewer is only licensed to receive ordinary domestic sewage. Anything else, water carrying fats, oils, food solids, silt, metals, chemicals, heat or strong pH, is trade waste, and discharging it needs written approval from your water authority before it goes down the drain.

A trade-waste agreement sets acceptance limits for what your discharge may contain and usually requires the waste to be pre-treated on site to meet them. The common pre-treatment devices each do one job:

• Grease arrestors hold wastewater long enough for fats and oils to float and solids to settle, so only the middle layer leaves. Kitchens and food processing need them, sized to the load and pumped out on a schedule.
• Oil and silt separators do the same job for wash bays, workshops and yards, catching hydrocarbons and sediment before the sewer or stormwater.
• pH correction and cooling bring strongly acidic, alkaline or hot discharges back inside the agreed window.

Pre-treatment only works if it is maintained. A grease arrestor that is never pumped out stops arresting grease and starts passing it straight through, and the first evidence is often a blocked sewer and a non-compliance notice arriving together.

06 Compliance, and the cost of getting it wrong

On an industrial site the regulations are not paperwork around the plumbing. They are the reason several of the systems exist, and the penalties for ignoring them fall on the business, not the contractor. Four obligations matter most, and each is administered by a different authority.

Discharge and pollution. Beyond the trade-waste agreement, larger or higher-risk premises hold an environment protection licence that sets conditions on what the site may discharge and emit. In New South Wales this runs under the Protection of the Environment Operations Act 1997, administered by the EPA; every state and territory has an equivalent regulator and law. Polluting waters can be an offence whether or not a licence exists.

Cooling towers and warm-water systems. Where a site runs a cooling tower or a warm-water system, it becomes a Legionella risk that is managed under AS/NZS 3666 and state public-health regulation. In NSW that means the system is registered with the local council, has a risk-management plan, and is sampled and tested on a set schedule, with high results reported quickly. This is specialist water-treatment territory, not general plumbing.

Work health and safety. Much industrial plumbing work happens in confined spaces or around hazardous chemicals, both of which carry their own WHS duties. For the site occupier the practical point is that this work needs trained, permitted people and a plan, and that is exactly why parts of it are never a do-it-yourself job.

07 Keeping it running, and who does what

Industrial water systems reward attention and punish neglect, and most of the attention they need is not plumbing at all. It is housekeeping, record-keeping and watching for change, and every bit of it is the site's own to do. The line between what you can manage and what needs a licensed plumber or specialist is clearer here than anywhere else in plumbing, because on an industrial site there is no grey middle where a confident amateur can help. It is either housekeeping or it is licensed work.

Predictive maintenance, honestly. Sensors that watch pressure, flow, temperature and vibration and flag a trend before a failure are genuinely useful on a system that runs continuously, because the earliest sign of most industrial failures is a slow drift in a number no one is reading. The caution is the same as anywhere: a dashboard is only worth what someone does with its alerts. The value is in the response plan behind the sensor, not the sensor itself.

08 Water worth saving

High-volume sites have the most to gain from using less, because on an industrial scale water is rarely just water: it has been pumped, treated, heated or chilled, and every litre saved saves that energy too. The moves that actually pay back, rather than the ones that only look green:

• Find the leaks first. On a large site a continuous leak can run unseen for months. Sub-metering the big users and watching overnight flow (which should fall to near zero) finds them faster than any upgrade.
• Reuse where the quality allows. Rinse water, cooling blowdown and treated effluent can often be recovered for a lower-grade use rather than sent to drain, provided the reuse is properly separated from the drinking supply with the same backflow discipline as section 02.
• Close the loop on cooling. Recirculating cooling instead of single-pass can cut a site's water use dramatically, with the trade-off that the recirculating loop then needs the Legionella management of section 06.
• Specify efficient fixtures in the amenities. The washrooms and kitchens on an industrial site are ordinary plumbing, and choosing WELS-rated tapware, toilets and urinals there is the same easy win it is anywhere. The star rating is a national scheme; more stars is less water for the same job.

09 When it is a licensed plumber's job

On an industrial site the answer to "should I get a professional in" is nearly always yes, because almost everything past housekeeping is licensed or accredited work by law. The more useful question is how to tell a contractor who understands industrial systems from one who does good domestic work and is out of their depth. Ask them:

• How will you protect the town main? A serious answer talks about the hazard rating of your site and the right class of testable backflow device, not just "a non-return valve".
• What does our trade-waste agreement allow, and does this change it? A contractor who works on industrial sites will ask about your agreement before they touch the discharge side, because changing it without the authority is their licence on the line as well as your compliance.
• What is the failure mode, and how will we see it coming? The best industrial work ends with you knowing what will wear out next and what to monitor, so a failure becomes a scheduled replacement.

Good industrial plumbing is quiet: it keeps clean water clean, gets used water safely away inside the rules, and leaves you with records and a maintenance plan rather than a recurring emergency. If you can describe the system you have and the problem you are seeing, the enquiry desk below can help you work out what you are actually looking at and what kind of licensed help it needs.

For the everyday commercial side of a mixed site, the amenities, kitchens, hot water and drainage that behave like a bigger version of a home, our commercial plumbing guide covers the ground this one leaves out, and the sustainable plumbing guide covers the water-efficiency thinking behind it.

10 Questions, answered

+ Related guides

This guide has no journal entries of its own; the industrial territory is covered here in one place. The neighbouring guides pick up where it stops: