Frequently asked questions about water pumps: selection, performance, depth, power consumption and spare parts

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Common questions about water pumps: selection, performance, depth, consumption and spare parts

Over the years of practice with customers who deal with water supply from a well, borehole, garden tank or need to pump water during construction work, the same questions keep coming up again and again. They are usually not difficult – the problem is that manufacturers and sellers rarely explain them in a way that makes practical sense. This article is an attempt to fix that. We will go through everything essential: how to choose the right type, what the technical parameters mean, what depth a suction pump can handle, how much electricity or gasoline it consumes and what to do if you need to replace spare parts.

If you are looking for a specific topic, also check out other articles in our Knowledge Centre – for example How to choose a water pump: gasoline, submersible or drainage? or Discharge and pump power: how to calculate what you need for a garden or well. Here we will focus on practical questions that customers ask most often – and on answers that really help in decision-making or in solving problems on site.

What type of pump do I actually need?

This is always the first question and at the same time the one where the most mistakes are made. People buy a surface self-priming pump and want to use it to draw water from 14 meters – it doesn't work. Or they acquire a powerful submersible pump that can handle the depth, but they don't have a sufficiently large diameter borehole and the pump simply won't fit. I have seen dozens of such cases in practice.

The basic division is simple:

Surface self-priming pumps – they stand on the surface, the suction hose goes down into the water source. Limited by suction depth, theoretically around 8–9 meters, in practice reliable up to 6–7 meters (depends on altitude, water temperature and the quality of seals).
Submersible pumps – they go entirely underwater. Depth is not a physical limitation – it is limited only by the length of the power cable and the overall discharge. These include well pumps, borehole pumps, as well as drainage sludge pumps.
Gasoline engine pumps – they have their own combustion engine, do not need electricity. Ideal where there is no power supply, or for higher performance for short-term pumping (fire hydrant, site drainage, flood, agriculture).
Drainage (sludge) pumps – they can handle water with contamination, sand, mud, small solid particles. They are not for drinking or utility water supply – they are for pumping out.

If you are not sure, look at the article Water pump vs. sludge drainage pump: what is the difference and when to use which – this issue is discussed in detail there.

What does discharge mean and why is it more important than power in kW?

The power of the pump in kW or watts indicates how much energy the motor consumes or produces. But what you are really interested in is discharge in meters and flow rate in liters per hour or minute. These two parameters determine whether the pump can handle your specific situation.

Discharge (also called manometric head) indicates how high the pump can push water. If you have a well 8 meters deep and you want to push the water into a tank that is 5 meters above ground, the total required manometric head is 8 + 5 = 13 meters (plus losses in the piping, which can be another 2–4 meters). You also need to add the horizontal distance – every 10 meters of horizontal piping is usually counted as an additional 1 meter of discharge.

Flow rate indicates how much water the pump can transport per unit of time. For a small garden irrigation (up to 500 m²) 1 500–2 500 l/h is sufficient. For a larger garden with turbines or sprinklers you need 4 000–8 000 l/h. For pumping out a flood or construction site, where you want to quickly pump out a large amount, you are looking for pumps with a flow rate of 10 000 l/h and more.

An important detail that manufacturers do not always emphasize: discharge and flow rate are inversely proportional. Every pump has so-called pump characteristic (Q-H curve). At maximum discharge, the flow rate is almost zero – the pump barely lifts the water, but almost nothing flows. At zero discharge (the pump is pumping horizontally without climbing) the flow rate is maximum. In practice, you always work somewhere in the middle of this curve.

What is the maximum depth from which a pump can draw water?

This is one of the most commonly misunderstood questions. The answer depends on the type of pump in question.

Surface self-priming pumps operate on the principle of vacuum. The physical limit for drawing water is determined by atmospheric pressure – at sea level, this is equivalent to approximately 10.33 meters of water column. In practice, there are losses in the piping, leaks at the joints, resistance from the suction basket, and water temperature. Result: a reliable suction depth is 6–7 meters, and a maximum depth for a well-installed pump with tight joints is about 8–9 meters. At greater depths, a surface pump cannot draw water by any force – it is not a matter of motor power, but of physics.

For depths exceeding 8 meters, you need a submersible pump. This pushes water up from the bottom – it does not create a vacuum, but rather a pressure. The discharge (i.e., to what height it can push water) depends on the pump itself. For example, the Submersible pump SKM 100 for wells and boreholes is specifically designed for use in wells and boreholes – it can pump water from depths where a surface pump simply cannot reach. It is important to check the diameter of the borehole (the typical minimum diameter for this type of pump is 4" = 100 mm), to ensure the pump fits inside the borehole.

Gasoline pumps are also surface pumps – the same physical limit for suction applies to them (6–8 m). Their advantage is not depth, but mobility and discharge performance. For example, the Gasoline pump H-BZP-30 with a discharge of 95 meters can push water to dizzying heights or very long horizontal distances – but only if it first draws the water, which is limited to a maximum depth of 7–8 meters.

How much fuel does a gasoline pump consume and when is it worth it compared to an electric one?

Fuel consumption of gasoline pumps depends on power and load. Approximate values from practice:

Small gasoline pumps (approx. 1–2 kW, e.g. BZP-10): consumption 0.5–0.8 liters per hour at full load. For garden use (not continuous operation), this means 1 liter for 1.5–2 hours of pumping.
Middle-sized pumps (approx. 3–5 kW, e.g. BZP-30 with 4850 W power): consumption 1.2–1.8 l/h. A 3.6-liter tank lasts 2–3 hours of continuous pumping.
High-performance pumps (approx. 7–10 kW, e.g. H-BZP-30 with 9690 W power): consumption 2.5–3.5 l/h at full power.

When is a gasoline pump worth it compared to an electric one? A simple answer: always when you don’t have electricity nearby, or when you need a portable solution that you can load into your car and take to a field, a garden without a power connection, a cabin without an electrical grid, a construction site, or during floods.

If you have electricity available and the pump will remain in one place (e.g., a garden house, a well pump house), an electric pump will be cheaper to operate and more convenient – it turns itself on and off, doesn’t require oil, a carburetor, or seasonal maintenance. You will read more about further comparisons in the article Gasoline water pump: what it is good for and when it is worth it compared to an electric one.

What affects pump performance in practice – conditions not included in the catalog by the manufacturer

Every catalog performance rating is measured under ideal laboratory conditions: clean water, optimal temperature, short piping, new seals, sea level altitude. In practice, it looks different.

Altitude: The higher you are, the lower the atmospheric pressure and the less a surface pump can draw. At 500 m above sea level, you lose about 0.5 meters of suction head, and at 1000 m above sea level, up to 1 meter. If you have a cabin in the mountains and a 7-meter deep well, you may have a problem where it would work perfectly fine at sea level.

Diameter and length of suction pipe: Too thin a pipe increases resistance and reduces the actual flow. For most garden pumps, a suction valve of at least 1" (25 mm) is recommended, ideally 1.25" (32 mm). Every elbow and joint also adds resistance – experts calculate each 90° elbow as 1–1.5 meters of equivalent pipe length.

Condition of the pump and age of the seals: Old, hardened seals in suction joints mean air leakage. The pump sucks in air instead of water, loses vacuum, and doesn’t pump – while the motor runs normally. This is a very common failure, especially after winter. The solution is simple: replace the seals (O-rings and flat gaskets), which is a cheap job costing 1–3 euros.

Temperature of the pumped water: Warmer water evaporates more easily inside the pump and reduces the efficiency of the suction process. Pumping cold spring water is more efficient than pumping water from a surface source heated by the sun in summer.

Water contamination: Every grain of sand or mud that passes through the pump damages the impeller. That is why a suction basket with a filter mesh is absolutely essential – not just a luxury option. If your suction mesh is missing or damaged, you are working against yourself.

Questions about submersible pumps: well diameter, cable, installation depth

Submersible well pumps are a technically more complex category. A few questions that appear most frequently:

What well diameter do I need? Standard submersible pumps for home use are manufactured for well diameters of 4" (100 mm) and 6" (150 mm). Most home wells have a diameter of 4" – before purchasing a pump, check with the well driller or in the well documentation. Physically, you cannot fit a 6" pump into a 4" well. A pump for a borehole (not a well) can be of a larger diameter – it depends on the clear diameter of the well. For details, see the article Submersible pump for a well or borehole: what diameter and depth match which pump.

How long a cable do I need? The cable must reach from the pump at the bottom of the well up to the electrical distribution board at the surface. Always allow a reserve of 3–5 meters – never cut the cable to the exact meter, because any modifications will cause problems. Connecting junction boxes underwater are not suitable unless they are specially certified – every bad connection increases the risk of an electrical short or shock.

Must the pump be fully submerged? Yes. Water cools the pump motor. If the water level drops below the pump level (for example, during high consumption or dry weather), the motor will overheat and be destroyed. Therefore, it is recommended to install the pump with sufficient reserve above the bottom of the well (20–30 cm to prevent silt from being sucked in) and to place it at least 1–2 meters below the expected lowest water level in a dry year. Some pumps have built-in thermal protection or dry-run protection – this is a feature worth paying extra for.

Must I always leave a drain valve on the pump? For submersible pumps in wells or boreholes, a check valve on the discharge pipe is recommended – it prevents backflow of water when the pump is turned off and also protects the home water supply from pressure surges. A drain valve is important for winterization, if you remove the pump for the winter.

Replacement parts: what wears out most often and where to find it

Pumps are mechanical devices – they wear out over time. The good news is that most common faults can be fixed with inexpensive replacement parts. The bad news is that for some exotic brands, replacement parts are simply not available – that is why choosing a device from an established manufacturer with available service is important.

What wears out most often:

Seals and O-rings – in surface pumps, these are mainly the seals of the suction and discharge nozzles, and the seal of the self-priming mechanism. Cost: 1–5 €, replacement is doable by yourself.
Suction basket with filter mesh – the mesh gets clogged or is mechanically damaged. Replacing the suction basket is simple and cheap (5–15 €). Don’t buy the cheapest one – a plastic suction basket with a coarse mesh will not stop fine sand, which then damages the impeller.
Impeller (impeller) – in cheaper pumps, it is often made of plastic and quickly wears out when pumping sandy water. Symptoms: the pump runs, but the flow and pressure drop significantly. Replacing the impeller is a major repair – sometimes it is cheaper to buy a new pump.
Mechanical seal (seal housing) – separates the wet part from the motor. When it wears out, water reaches the motor, which leads to bearing damage or a short circuit. Signs: dripping from the pump shaft area, rapid bearing wear. Replacement requires disassembling the pump and professional intervention – in service 30–80 €.
Capacitor (for single-phase electric motors) – the capacitor is used to start the motor. When it fails, the motor buzzes, heats up, but does not start, or starts slowly. Replacing the capacitor is a common and cheap repair (the capacitor costs 3–15 €, replacement is simple).
Carburetor and spark plug (gasoline pumps) – after each season, check and clean the carburetor and replace the spark plug if necessary. A clogged carburetor is the most common reason why a gasoline pump will not start after winter. Carburetor cleaning spray (4–8 €) and a new spark plug (2–4 €) will solve most problems.

When choosing replacement parts, always follow the pump model number, not just visual similarity. An impeller with a diameter of 95 mm and 97 mm looks the same, but functions completely differently. When ordering, always provide the full model code of the device – for example, from the production label.

For more detailed information on what to do when the pump stops working properly, see the article Common pump failures: why it doesn’t pump, loses pressure or overheats.

How long does a pump last and what prolongs its lifespan?

A quality pump from a reputable manufacturer should last 10–15 years under normal use without major repairs. In practice, this depends on three factors: the quality of the device itself, the operating conditions, and how well you take care of the pump.

What shortens the lifespan:

Pumping sandy or heavily contaminated water without a strainer
Dry running (the pump runs without water – the mechanical seal and impeller overheat)
Frequent short starts (the pump turns on and off multiple times per minute – overloads the motor)
Winterization with water in the pump body (frozen water cracks the pump casing)
Improper installation (too thin piping, missing check valve, misalignment of the coupling)

What prolongs the lifespan:

Proper winterization – draining water and storing indoors (garage, basement)
Regular oil changes for 4-stroke gasoline pumps (every 25–50 motor hours)
Checking and replacing the strainer every season
Installing a pressure tank (membrane tank) for home water systems – reduces the number of starts
Protection against dry running – float switch, level sensor, or manual monitoring of the water level

Detailed procedures for winterization and overall maintenance can be found in the article Maintenance and winterization of a pump: how to extend the lifespan of gasoline and submersible pumps.

Gasoline pump for clean vs. utility water – what is the difference?

Not every gasoline pump is suitable for pumping drinking water. Most gasoline pumps are certified for clean and utility water – this means that the materials of the pump body (aluminum, cast iron, plastic) are not necessarily certified for direct contact with drinking water. This is not a problem for garden irrigation, filling a pond, flood control, or industrial use. If you are filling a drinking water tank, verify the material certification – the manufacturer must include this in the documentation.

For example, the Gasoline pump BZP-20 is explicitly designed for clean and utility water – this distinction is important when choosing. Sewage pumps are specially designed for water with contamination and should not be used for pumping drinking water or garden irrigation of vegetables.

Questions about electric vs. gasoline pumps: power, pressure, and operating cost

Customers often ask why a gasoline pump has a higher pressure and flow rate than an electric one at the same price. The answer is simple: a gasoline engine is more powerful in the same price category than an electric motor. A gasoline engine with a power of 6–10 kW actually costs less than an electric motor of the same power including the electrical panel and cabling.

Disadvantages of gasoline pumps compared to electric ones:

Noise (gasoline engines are significantly louder)
Exhaust fumes – cannot be operated in enclosed spaces
Regular maintenance (oil, spark plug, carburetor, air filter)
Dependence on fuel supply
Higher operating cost during long-term continuous operation
Cannot be automated with a pressure switch (must be constantly monitored)

For a garden water supply or a family home, an electric submersible pump + pressure tank is a much more convenient solution. A gasoline pump is a tool – very useful in certain situations, but not an ideal solution for everyday water supply.

Most frequently asked questions (FAQ)

Why is my pump not pumping, even though the motor is running normally?

The most common reason is loss of vacuum in the suction system – this means that air is entering somewhere in the suction system. Check all connections on the suction pipe to see if any seals are loose or cracked. Another possibility is an empty pre-chamber (the pump needs to be filled with water before starting – so-called priming). If the water level is lower than 7–8 meters, a surface pump simply cannot reach it. More in the article Common pump faults: why it doesn't pump, loses pressure, or overheats.

Can I use the pump to pump water with contamination (mud, fine sand)?

It depends on the type of pump. Standard surface and submersible pumps for clean or utility water can handle only minimal contamination – fine mechanical impurities quickly wear them out. For water with mud, sand, or small solid particles, sewage (drainage) pumps are designed, which have more durable impellers and larger passages for solid particles. More about the differences in the article Clean water pump vs. sewage pump: what is the difference and when to use which.

What diameter of suction and discharge pipe should I use?

Always follow the manufacturer's specified diameter of the pump inlet – this is the minimum diameter. It is not an error to use a slightly larger diameter pipe (e.g., 1.25" instead of 1") – a larger diameter reduces resistance and improves flow. The pipe is then reduced to the pump inlet using a reducer. Never use a smaller diameter than the inlet – it unnecessarily restricts the pump and reduces its performance.

How long can a gasoline pump run continuously?

Most 4-stroke gasoline pumps are designed for long-term operation – theoretically as long as there is fuel. In practice, I recommend taking a 15–20 minute break every 2–4 hours of continuous operation to check the oil level and motor temperature. Some models require oil level monitoring every hour. See the instructions for the specific model – for example, for BZP-30, the operating parameters are clearly stated in the manual.

Do I need to remove the submersible pump from the well in winter?

It depends on the depth of the well and local winter conditions. If the well does not freeze (the water level is below the frost line, which is usually 80–120 cm below the surface in Slovakia), the pump can remain in the well all winter. You just need to ensure that the piping above ground and in unheated areas does not freeze – thermal insulation or draining the water from the piping. If the well is shallow (up to 2 meters deep) or you are concerned about frost, it is better to remove the pump and store it indoors.

What is a pressure tank and do I need it with the pump?

A pressure (membrane) tank is an accumulator that stores water under pressure. When you open the tap, water is first drawn from the tank – the pump does not start. The pump only starts when the pressure drops below the set threshold. Without a pressure tank, the pump starts every time you open the tap – even for a few deciliters – which is very harmful to the motor (frequent starts strain the winding and capacitor). For a home water supply, a pressure tank is almost a necessity, not a luxury. The recommended tank capacity is at least 20–50 liters for a typical household.

Conclusion: a few practical recommendations before buying

A pump is an investment for years – it doesn't pay to save in the wrong place. Before buying, determine the answers to these questions: From what depth will you be pumping? What flow rate do you actually need (calculate your garden, household, consumption)? Do you have an electrical connection at the installation site? What is the quality of the water (clean, sandy, with mud)? Do you need a portable solution or a fixed installation?

Answers to these questions will naturally guide you to the right type. If you need help calculating the pressure or choosing a specific model, see the article Pressure and power of a pump: how to calculate what you need for a garden or well – there you will find specific formulas and examples. And if you already have a pump and are dealing with installation, the articles Installation of a submersible pump in a well or borehole: step-by-step guide or Installation of a gasoline pump: wiring, suction strainer, and first start will help you.

The full range of pumps including gasoline, submersible, and drainage pumps can be found on the Pumps category page – each product has detailed parameters from which you can determine whether it fits your situation.

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