Firefighter Mechanical Aptitude: One Water Pressure Question, Worked Step by Step

In still water open to the air, the reading on a pressure gauge depends only on how far below the water's surface it sits, measured straight down. A water pressure question may show a tank, a hill, a long pipe and several numbers, but most of those numbers do not affect the answer.

This post explains that rule and the physics behind it, works through an original hydraulics question step by step, explains why each wrong answer is wrong, and covers what changes once the water starts to move.

What sets water pressure in a firefighter aptitude question?

In still water, pressure depends only on depth: how far a point sits vertically below the open water surface. Fresh water adds about 9.8 kilopascals (kPa) for every metre of depth, a figure often rounded to 10 kPa per metre for quick arithmetic. The shape of the tank, the amount of water, and the width, length and route of the pipe do not change the reading.

The reason is weight. Picture a thin column of water standing on a small patch of the tank floor. The pressure on that patch is the weight of the column divided by the patch's area, and a taller column weighs more. Double the depth and the pressure doubles; move sideways at the same depth and nothing changes.

Two more facts help before any arithmetic:

• Pressure in still water pushes equally in every direction. A gauge on a side wall reads the same as one on the floor at the same depth, whichever way the gauge faces.
• An ordinary pressure gauge reads pressure above the surrounding air. That is why it reads zero at the open surface of a tank and starts climbing as soon as it goes below it.

If a question works in feet and pounds per square inch (psi), the same rule runs at about 0.43 psi per foot. Use whichever figure the question gives you.

Why doesn't the shape of the container matter?

Because the container's walls make up the difference. At a given depth in connected, still water, the pressure is the same whether the water sits in a wide tank, a narrow pipe or an oddly shaped vessel, so two gauges at the same level read the same even when one container holds far more water than the other.

This can seem wrong, because the wide tank holds more water and so more weight. But in a tank that flares outward toward the top, the sloping walls hold up the extra water. In one that narrows toward the top, the walls press down on the water beneath them. Either way, the floor ends up under the same pressure it would feel beneath a straight column of the same height.

What a bigger tank does change is total force and supply. Force is pressure multiplied by area, so a wide tank floor carries more total force than a narrow one at the same pressure. More water also means the supply lasts longer before the surface drops. Neither changes what a gauge reads.

The height of the water surface does change the reading. Drain enough water to lower the surface by one metre and every gauge below it reads about 10 kPa less. The same logic is why water in connected vessels settles at one level: if one side stood higher, the bottom on that side would be under more pressure, and water would flow until the levels matched.

How does elevation change hose and hydrant pressure?

Every metre water climbs costs about 10 kPa, and every metre it drops adds about 10 kPa. A hydrant at the foot of a hill fed from a tank at the top has more pressure than one halfway up, and a nozzle taken up a stairwell has less pressure than the pump outlet below it, even before friction is counted.

This is the same depth rule applied to elevation. A gravity-fed water tower supplies pressure because its water surface stands above the streets it serves, and the higher that surface sits above a given hydrant, the higher the hydrant's static pressure.

For hose work, the rule applies uphill and downhill. A line stretched 10 metres up a slope or a stairwell arrives with roughly 100 kPa less than the pump is giving it, from height alone, so the pump has to make up the difference. A line run downhill picks up pressure on the way.

Can you solve this water pressure question?

The key is measuring the right height. Work it on paper before reading on; we wrote the question for this post.

A rural water system stores water in an open-topped tank on a hill. The tank holds about 400,000 litres, and its water surface is 30 metres above Hydrant X at the bottom of the hill. Hydrant Y stands on a terrace 12 metres higher than Hydrant X. It is fed by a narrower pipe that winds 150 metres down the slope from the tank. Both hydrants are closed, and no water is flowing anywhere in the system. Using 10 kPa per metre, what does a pressure gauge on Hydrant Y read?

• A. 120 kPa
• B. 180 kPa
• C. 300 kPa
• D. 1,500 kPa

How do you work out the answer?

The answer is B, 180 kPa. Hydrant Y sits 18 metres below the water surface in the tank, because 30 metres minus 12 metres is 18, and 18 metres of water at 10 kPa per metre gives 180 kPa. Here is the reasoning in order.

Step 1: Find the reference level. The tank is open to the air, so a gauge would read zero at its water surface. Every height that matters is measured down from that surface, not up from the bottom of the hill.

Step 2: Find Hydrant Y's depth below the surface. The surface is 30 metres above Hydrant X. Hydrant Y is 12 metres above Hydrant X, so it sits 30 minus 12, or 18 metres, below the surface.

Step 3: Turn depth into pressure. 18 metres multiplied by 10 kPa per metre is 180 kPa. With the more precise 9.8 kPa per metre it comes to about 176 kPa, which is why a question tells you which figure to use.

Step 4: Cross out the distractors. Three details in the question do not affect the answer.

Detail in the question	Does it change the static reading at Y?	Why not
The tank holds about 400,000 litres	No	Volume decides how long the supply lasts, not the pressure
Hydrant Y's pipe is narrower	No	In still water, pipe width does not change the pressure at a given depth
The pipe winds 150 metres down the slope	No	Only the vertical drop counts, not the length or route of the pipe

Step 5: Check against Hydrant X. Hydrant X sits 30 metres below the surface, so it reads 300 kPa. Hydrant Y stands higher, closer to the surface, so it must read more than zero and less than Hydrant X. 180 kPa meets both conditions.

Why are the other answers wrong?

Each wrong answer comes from a specific measuring mistake that is easy to make when the drawing has many details.

• A, 120 kPa, treats Hydrant Y's height above Hydrant X, 12 metres, as if it were a depth. It measures up from the bottom of the hill instead of down from the water surface, which reverses the rule: the higher a hydrant stands, the less pressure it has.
• C, 300 kPa, is the reading at Hydrant X. It uses the full 30 metre drop from the tank and forgets that Hydrant Y is 12 metres up the hill from there.
• D, 1,500 kPa, measures along the pipe: 150 metres multiplied by 10 kPa. Pressure from height depends on the vertical drop alone, and Hydrant Y sits 18 metres below the water surface however far the pipe winds to reach it, so a straight pipe would give exactly the same static reading.

What happens to the pressure once the water flows?

It falls. Open Hydrant Y and the water moving through the pipe loses pressure to friction, so the gauge drops below its 180 kPa static reading; the pressure left while water is flowing is called residual pressure. At the same flow, a narrower or longer pipe loses more, which is where the pipe details in the question would finally matter.

So the depth rule in this post describes still water: closed hydrants, a charged line with the nozzle shut, a tank at rest. Read each question for which of the two situations it describes. When a question says water is flowing, height still counts at about 10 kPa per metre, but friction loss comes on top of it, and a narrow pipe leaves the far end with lower pressure than a wide one would.

Do firefighter aptitude tests ask about water pressure?

FireTEAM's official description names it. As of October 2026, the National Testing Network (NTN) says most questions on its FireTEAM mechanical test concern "basic mechanical objects and principles such as valves and water pressure." Other official descriptions list mechanical reasoning without naming topics, and Ontario's OFAI Stage One test lists no mechanical section.

Here is what each official description says, as read in October 2026:

Test	What its official page says about mechanical content
NTN FireTEAM	A multiple-choice test shown on video, with questions about an animated brick-making factory; valves and water pressure are its examples of what most questions cover, and candidates also troubleshoot by watching the system run
NTN Firefighter (Express) Exam	Tests mechanical reasoning and aptitude, with a picture on every item; no topics are listed
Edmonton Fire Rescue Services aptitude test	Lists maps, diagrams and mechanical reasoning among the skills it assesses
OFAI Stage One FACT (Ontario)	Lists Reading Ability, Mathematical Reasoning, Map Reading, Writing Ability and Personal Characteristics, with no mechanical section

Two notes on the Canadian departments, both read in October 2026. The Calgary Fire Department's careers page names NTN as its aptitude test vendor and describes a two-part online exam, without saying which NTN test that is. Edmonton's recruitment page puts the aptitude test at 40 percent of the overall score, while warning that its 2027 intake process is being reworked, so reread that page before you rely on the figure.

NTN also says every FireTEAM mechanical question can be answered from common sense and from watching how everyday objects work. Depth and elevation questions fit that description: once you know the rule, the arithmetic is one subtraction and one multiplication.

What is a fast method for water pressure questions?

Use the same five steps every time. They take seconds and catch each of the mistakes behind the wrong answers above.

1. Find the open water surface, where a gauge would read zero.
2. Measure straight down from that surface to the point the question asks about, subtracting heights when the point sits partway up a hill or a building.
3. Multiply by the figure the question gives, such as 10 kPa per metre.
4. Cross out tank size, pipe width and pipe length, unless the question says water is flowing.
5. Check the direction: a higher point reads less than a lower one on the same supply.

Where can you practise more water pressure questions?

Depth and elevation problems like the one above are part of Semparo's 500-question mechanical bank, alongside levers, pulleys, gears, tools and valves, and every answer comes with its reasoning. You can start the mechanical bank at no cost, with 10 sample questions.

On test day, water pressure questions appear alongside other topics and sections. Our timed practice battery gives mechanical 15 questions and 15 minutes beside human relations, math and reading, written in the FireTEAM style and drawing fresh questions every sitting. NTN publishes only a rough two-hour total for the whole test, so the per-section clock is our own choice.

The full bank, the syllabus lesson on hydraulics and pressure and the timed mock require the Aptitude section or Pro; compare the two on the pricing page.