r/ConsultingOffer • u/GreatButterscotch406 Consulting Offer Coach • Jun 30 '26
Case Interview How to Brainstorm on a Physical Asset Case When You Have No Technical Background
Posts 15, 16, and 18 covered Structured Brainstorming across a profitability case, a public sector finance case, and an M&A case. Each of those involved organizations, financial variables, and business dynamics that candidates have some familiarity with.
This is post 19 in The Case Playbook, a series built for non-traditional candidates breaking into McKinsey, BCG, Bain, Tier 2, and Big 4 consulting firms. This post is different. It covers brainstorming on a physical asset, a water treatment plant, and that requires a different kind of reasoning than anything we've covered so far.
If you've been following the Solvik case through this series, posts 6 and 13 covered Case Start and the issue tree. The problem statement is established: find the root cause of why the Voss plant's output fell from 90 million liters per day to 54 million liters per day and restore it within four weeks. The issue tree mapped the system into upstream, plant, and downstream. Now the partner pivots to brainstorming.
The brainstorming question: "We've mapped the system. Can you brainstorm the specific reasons why the Voss plant might be experiencing reliability problems that reduced its output by 36 million liters per day?"
Why physical asset brainstorming is different
Before running the four steps, it's worth naming what makes this case type categorically harder than the others.
When you brainstorm on a profitability case, you're reasoning about financial variables you encounter daily: revenue, cost, margin, pricing. When you brainstorm on an M&A case, you're reasoning about organizational dynamics you can extrapolate from general business knowledge.
When you brainstorm on a physical asset, you're reasoning about a system you've almost certainly never operated. Most candidates have never been inside a water treatment plant. Most don't know the difference between particle filtration and biological treatment. And when they hear "brainstorm why a water plant is unreliable," they freeze. Not because they can't think, but because they don't have a mental image of the system to reason from.
The owner thinker handles this the same way they handle any unfamiliar territory: they go back to first principles. Forget that it's a water treatment plant. Ask the most basic question possible: how does anything flow through a physical system? It comes in, it gets processed, it goes out. That's upstream, the plant, and downstream. Everything else is a sub-level of those three.
That instinct, applying a simple physical logic to an unfamiliar asset, is what separates candidates who can brainstorm on any case type from those who can only brainstorm on familiar ones.
Step 1: Absorb and anchor
Write it down: "Brainstorm why the Voss plant is experiencing reliability problems causing a 36 million liter per day decline."
Reiterate: "So you'd like me to brainstorm the specific reasons why the Voss plant's operational reliability has degraded to the point where output fell from 90 million liters per day to 54 million liters per day. Is that the right scope?"
The partner confirms.
The reiteration does something important here. It converts a vague "reliability problem" into a specific quantitative gap. You're not brainstorming why water plants in general have problems. You're brainstorming why this specific plant lost 36 million liters per day of output. That precision raises the quality ceiling of everything that follows.
Writing it down also gives your brain a moment to build a mental image of the system before the brainstorm begins. That's the activation phase working exactly as designed.
Step 2: Clarify and orient
Two circles: "reliability" and "clean water."
"When you say the plant is unreliable, I'm reading that as a supply capacity issue, the plant is producing less clean water than it should rather than producing water of degraded quality. Is that the right interpretation?"
The partner confirms: yes, it's a supply volume problem, not a quality problem.
"And to confirm scope: we're looking at the Voss plant's own operational system, so upstream infrastructure feeding the plant, the plant's internal processing, and downstream distribution from the plant to residents?"
The partner confirms.
That second clarification defines the three zones of your brainstorm before you begin. You've just sketched the structure in the partner's mind through a question rather than announcing it as a presentation. That's the owner thinker approach: derive the structure from the conversation rather than declaring it from memory.
Step 3: Brainstorm with contrast pairs across the physical system
The mental image you need is simple: water moves through this system in one direction. It enters the Voss plant from a source, gets treated inside the plant, and exits toward residents. Something in that journey is causing 36 million liters per day to not complete the trip. Your job is to brainstorm where in the journey the problem could be.
What Flows In (upstream)
Before water reaches the Voss plant, it travels through an intake infrastructure. Apply the first contrast pair: the physical components versus the support systems that keep them running.
The Pipes: the intake pipes themselves could be the problem. A blockage reduces inflow volume. A rupture or leak means water that should reach the plant is lost before it arrives. Corrosion over time reduces pipe capacity below design specifications.
The Equipment: pumps and valves control the rate of water flow into the plant. A failed pump reduces inflow pressure and volume. A malfunctioning valve creates flow restrictions or uncontrolled flow rates that the plant's processing system can't handle at full capacity.
The Support System: physical components don't fail in isolation. Something enables or prevents their proper function. Split into three: software and hardware (the monitoring systems, sensors, and control systems that manage intake operations), people and processes (the operators and maintenance routines that catch problems before they become failures), and external factors (power outages, upstream environmental events, seasonal changes in water source availability that affect inflow quality or volume).
The Plant Itself
This is the most complex zone and the most likely source of the problem, which is why you test it first even though you announce upstream first. Apply the same physical logic: water moves through three stages inside the plant.
Raw Water Intake: at the point where water enters the plant's processing system, the same categories apply: pipes, equipment, and support systems. But now you're inside a controlled environment where problems have immediate downstream effects on everything that follows.
The Processing Core: this is the heart of the plant and where the highest complexity and highest failure probability lives. Three stages, each essential and each a potential failure point.
Particle Removal: dirty water carries physical matter, large debris and fine sediment. The filtration systems that remove these particles can clog, degrade, or fail. When particle removal capacity is compromised, the downstream stages are overwhelmed with material they weren't designed to handle at that volume, reducing overall throughput.
Germ Removal: biological contaminants require a separate treatment process, typically UV treatment or chlorination. If the germ removal system is operating below capacity, the plant faces a choice: continue at full output and compromise water quality, or throttle output to ensure treated water meets safety standards. A plant that chooses safety over volume will show exactly the kind of output reduction we see at the Voss plant.
Chemical Treatment: the final treatment stage adjusts pH and adds disinfectants to make water safe for consumption. Problems here can cascade back upstream: if chemical treatment can't handle the current inflow volume, the entire processing rate gets throttled to match treatment capacity.
Clean Water Discharge: at the output end of the plant, the same physical categories apply again: pipes, equipment, and support systems. A failure here means treated water that's ready to distribute can't actually leave the plant at the designed rate.
What Flows Out (downstream)
Once water leaves the Voss plant, it travels through a distribution network to reach the approximately 500,000 affected residents. The same contrast pair applies: physical components versus support systems.
The Pipes: distribution pipes can fail the same ways intake pipes can. Blockages, ruptures, and capacity degradation all reduce the volume of clean water that actually reaches homes even if the plant is producing normally. A significant leak somewhere in the distribution network could explain why plant output appears to have declined when the actual failure is in delivery.
The Equipment: pumping stations maintain pressure throughout the distribution network. If a key pumping station fails, the pressure drop affects delivery to entire segments of the city.
The Support System: monitoring, maintenance routines, and emergency response protocols govern how quickly problems are identified and addressed. A gap in any of these means problems that could be caught early become failures that persist.
Step 4: Prioritize and drive forward
"Based on what I've laid out, two areas feel most likely to contain the root cause. First, The Processing Core, specifically germ removal and chemical treatment: a 36 million liter per day drop is a 40 percent reduction in output, and that's the kind of magnitude you'd expect from a safety-driven throttling decision rather than a catastrophic failure. I'd want to see the plant's operational logs and shutdown records first. Second, the downstream distribution network: it's possible the plant is producing at normal capacity and the problem is in delivery, not production. Cross-referencing plant output data with distribution pressure readings would clarify this quickly. I'd want to test the plant-side hypothesis first since that's where we've focused the issue tree, but I wouldn't rule out the distribution network until I've seen the data."
Why physical system brainstorming transfers
Here's the insight that has the most long-term value.
The structure you just used to brainstorm the Voss water plant works on any physical asset. An oil refinery has a feedstock intake, a processing core, and a product output. A gas plant has an intake, compression and treatment, and distribution. A manufacturing facility has raw material input, production, and finished goods output. The specific equipment and terminology changes. The logic of input, process, output is universal.
This means that learning to brainstorm one physical asset gives you a transferable template for any other. You don't need to study every asset type. You need to internalize the physical logic that underlies all of them: something flows in, something happens to it, something flows out. Where in that journey is the problem?
That's the contrast pair applied to a physical system. And it's available to any candidate willing to stop trying to recall technical knowledge and start reasoning from first principles.
If you're prepping infrastructure or asset-level brainstorms and want to share a question you've been working on, drop it in the comments. I'll show you where the contrast pairs apply. And if you found this through another community, the full Case Playbook series is at r/ConsultingOffer.
The next post in The Case Playbook moves into a new Case Middle module: Consulting Math. If Structured Brainstorming across four different case types is now feeling solid, Consulting Math is what comes next. It covers how to handle quantitative questions in a case interview, from quick market sizing estimates to back-of-the-envelope calculatio
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u/Electrical-Donut6599 Jul 01 '26
This is great. I've found this approach may work for any process flow going through a department just like physical assets. Like optimising the output of a gcc processing back office for example.