How to choose the power and head of a pump according to well depth

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Why well depth is a key parameter when selecting a pump

When customers come to us with the question "what pump should I buy for my well," the first thing we ask is not the brand or the price, but the depth of the well or borehole and the water level. These two pieces of information directly determine what lift the pump must achieve, and from this the selection of the power class, pump diameter and motor type depend. An incorrectly estimated lift is one of the most common causes of dissatisfaction - the pump either cannot push the water to the required location, or on the contrary, you unnecessarily overinvest in power that you will never use and pay extra for electricity.

When selecting a pump for a well, we encounter two basic physical quantities - suction head (respectively the depth below the water level from which the water is pumped) and discharge head (the height and distance to which the water must be delivered after being pumped from the pump). The sum of these values, plus friction losses in the pipes and fittings, gives the so-called total head, which we must work with when selecting a specific model.

Basic terms: total head, flow rate and pump characteristic

Before we get into specific recommendations according to depth, it is important to clarify terminology, as a large part of misunderstandings when selecting a pump arise precisely from confusion between these terms.

Total head (H) - given in meters and expresses the height to which the pump is able to deliver water at a given flow rate. It is not just the physical height of the level above or below the pump, but the sum of all height differences and resistances in the system.
Flow rate (Q) - the amount of water the pump delivers per unit of time, usually in liters per minute (l/min) or cubic meters per hour (m³/h).
Pump characteristic - a graph of the dependence of total head on flow rate. Each pump has its own curve - at zero flow (closed valve) it achieves maximum total head, which decreases with increasing flow rate.
Static water level - the water level in the well at rest, without pumping.
Dynamic water level - the water level during pumping, which is always lower (deeper) than the static one, because the water is replenished from the surrounding ground more slowly than you are pumping it out.

Exactly the difference between static and dynamic water levels is a common reason for underestimating the required power. If the well has a static water level of 8 m, but during longer pumping it drops to 14 m, the pump must be dimensioned for the worse, dynamic value - otherwise the pump may run dry, which in most cases leads to damage.

How to calculate the total head

The total head that the pump must overcome consists of three components:

Geodetic suction head - the distance from the water level (dynamic) to the pump, or to the point where the water enters the system.
Geodetic discharge head - the distance from the pump to the highest point of water withdrawal (e.g., a tap in the bathroom on the first floor, or a pressure tank in the technical room).
Friction losses - the resistance that water overcomes in the pipes, through elbows, valves, filters and fittings. With longer pipelines (over 30-40 m) or when using narrower hoses (e.g., 1" for long distances), these losses can amount to several extra meters.

Practical example: we have a borehole with a dynamic water level at 25 m, the pump is suspended at a depth of 30 m (a safety margin below the dynamic water level), the discharge pipe leads to a house 40 m away and the water must be delivered to a pressure tank in the basement, practically at ground level, plus to a tap on the roof at 6 m height. The total head will therefore be approximately: 30 m (pump depth) + 6 m (height in the house) + friction losses (about 2-4 m for 40 m of pipe and several elbows) = about 38-40 m of required total head. The pump must be dimensioned for this value with a certain reserve, ideally 15-20 %.

Approximate table for selection according to well depth

The following table is based on experience from typical implementations for family homes with standard consumption (family of 3-5 people, occasional garden irrigation). These are approximate values - the specific selection always depends on the diameter of the borehole, the required flow rate and the length of the discharge pipe.

Well/borehole depth	Recommended total head of the pump	Type of pump	Note
up to 8 m	15-25 m	surface or submersible	surface pump with suction is also possible if the well is close to the house
8-15 m	25-40 m	submersible (2" or 3")	surface pumps are already at the limit of suction capacity
15-30 m	40-70 m	submersible (3" centrifugal)	typical range for boreholes in family homes
30-50 m	70-110 m	submersible screw or multi-stage centrifugal	also suitable pumps with a higher number of impellers
50-80 m	110-160 m	submersible screw pumps for narrow boreholes	screw principle handles large total heads at lower flow rates
over 80 m	160 m and more	specialized high-pressure submersible pumps	individual consultation and precise hydrogeological survey are necessary

Centrifugal vs. screw pumps - difference in approach to total head

At greater depths, it is important to distinguish between two construction principles of submersible pumps, as each approaches the total head differently.

Centrifugal (centrifugal) pumps work with multiple impellers connected in series (stages). Each stage contributes a certain amount of total head, so the resulting head is the sum of the heads of the individual stages. These pumps usually provide a higher flow rate at medium total head and are suitable for boreholes with a diameter of 3" and more, where there is enough space for a wider pump body.

Screw (progressive) pumps use the principle of a rotating screw in a flexible rubber insert (stator), which "moves" the water in a smooth, almost pulse-free flow. This principle allows achieving very high total heads even at a small pump diameter, which is ideal for narrow 2" boreholes. For this advantage, you pay for a lower flow rate compared to centrifugal pumps of the same power class, but for normal household consumption this is usually sufficient. A typical example is Submersible screw pump for narrow boreholes STING 2", which is specifically designed for situations where the borehole is narrow but deep, and a classic centrifugal pump would either not fit or would not achieve the required head.

The more detailed differences between these two principles are also discussed in the article Submersible pump: Vane vs. Centrifugal - Differences and Applications, where you will also find specific recommendations according to the type of well.

Practical examples from everyday implementation practice

Over the years of selling pumping equipment, certain typical situations repeat themselves. Below we present a few specific scenarios that will help you orient yourself in your case as well.

Scenario 1: Dug well near a family house, depth 6 m, water level at 4 m

This is a classic older dug well with a large diameter (often 80-100 cm), where the well diameter is not a limiting factor. The house is 15 m away, and the water level in the bathroom on the upper floor is 5 m. The total required delivery head is approximately 4 (water level) + 5 (house height) + 2 (friction losses) = 11 m, and with a safety margin we choose a pump with 20-25 m delivery head. There is also room for a surface pump placed in a shaft or in a technical room, or for a simple submersible pump suspended in the well. Due to the large diameter of the well, it is not necessary to solve the issue of a narrow borehole.

Scenario 2: 3" well, depth 20 m, dynamic water level 12 m

This is one of the most common cases in new constructions with garden irrigation and house supply. With a dynamic water level of 12 m, a delivery to the house at a distance of 25 m and a height difference of 4 m in the house, the required delivery head is approximately 12 + 4 + 3 (losses) = 19 m, and with a safety margin we choose a pump of about 35-45 m delivery head at a flow rate of 40-60 l/min, which also covers peak consumption during irrigation. In this case, a centrifugal pump for a 3" well is ideal, for example Submersible pump IBO 3" STM 20, which is designed precisely for this type of application - sufficient flow rate for the household and garden at medium depths.

Scenario 3: Narrow 2" well, depth 45 m, dynamic water level 30 m

In narrow wells, where the diameter of the casing pipe is only 110-125 mm, the options for pump selection are significantly limited - a standard 3" centrifugal pump physically cannot fit there. In this case, a vane pump is almost the only reasonable option. With a dynamic water level of 30 m and a delivery to the house with a height difference of 5 m, the required delivery head is approximately 30 + 5 + 4 (losses in a longer pipeline) = 39 m, and with a safety margin we choose a pump with a delivery head of 60-70 m. Specifically for such a task, the Submersible vane pump for narrow 2" well STING 2" is intended, which can deliver water from greater depths even with a small diameter.

Scenario 4: Deep well over 60 m with variable dynamic water level

In deeper wells, we increasingly encounter the situation where the hydrogeological survey indicates a dynamic water level around 45-50 m, but during longer pumping (for example, during a dry summer), the water level drops even further. In such cases, we recommend not only choosing a pump with sufficient delivery head reserve (often 130-150 m), but also considering the installation of a float or electronic dry-run protection switch, which automatically turns off the pump when the water level drops below a safe level. We elaborate on this topic in more detail in the article on the most common faults of submersible pumps, where dry running is listed among the main causes of premature motor failure.

How to take into account also the water quality and sand content

Depth and delivery head are not the only parameters that decide the choice - the quality of the pumped water is also important, specifically the content of mechanical impurities (sand, silt, small rock particles). This is a typical problem with newly drilled wells, where the well has not yet "stabilized" and during pumping, it pulls fine particles from the surrounding ground.

If the water contains an increased amount of sand, we recommend installing a Sand separator filter 1" for suction in the system before the pump or immediately after the discharge, which captures mechanical impurities and protects the pump impeller, valves, and subsequent pipelines and appliances (for example, a water heater or washing machine) from wear. Sand is one of the most common causes of premature wear of impellers and bearings, regardless of how high quality and properly dimensioned a model you have chosen.

Well diameter and its relation to performance and delivery head

It is impossible to talk about delivery head without mentioning the well diameter, because these two parameters influence each other. Only a limited range of pumps with a smaller body diameter (typically up to 45-50 mm) can physically fit into a narrow 2" well, which also limits the maximum achievable flow rate at a given delivery head. In a 3" and larger well, more powerful centrifugal pumps with a higher flow rate at the same delivery head can already fit.

This means that in deep but narrow wells, you sometimes have to accept a lower flow rate than you would get at the same depth but with a wider well diameter. This topic is discussed in detail in the articles What well diameter do you need: the difference between 2", 3" and 4" pumps and What pump diameter do you need - 2" or 3" well, where you will also find specific dimensional tables.

How to calculate with a reserve and why it makes no sense to "precisely" dimension

A common mistake in independent calculation is the attempt to dimension the pump exactly according to the current measured values. We do not recommend this in practice, for several reasons:

The dynamic water level changes throughout the year, especially depending on precipitation and groundwater extraction in the area (agriculture, neighboring wells).
Pipes gradually become clogged with sediments and scale, increasing friction losses.
The household gradually adds new consumption points - garden irrigation, pool, another bathroom - increasing the required flow rate and pressure.
A pump operated at the edge of its maximum characteristic wears out faster and has a shorter lifespan.

The recommended reserve is usually 15-25% above the calculated delivery head value, and for flow rate we choose a pump so that the operating point (the intersection of the pump and pipe characteristics) lies in the central, most efficient part of the performance curve, not at its edge.

Step-by-step guide to selecting a pump

For a summary, we present a practical procedure that we also use in our own consultations with customers:

Determine the exact depth of the well/borehole and especially the dynamic water level (if you don't have a hydrogeological survey, it can be roughly estimated by test pumping).
Measure or estimate the distance and elevation difference between the well and the point of use (house, garden).
Estimate the length of the discharge pipe and add friction losses (roughly 1-2 m for every 10 m of pipe at a standard diameter).
Sum up all the values and add a reserve of 15-25 %.
Determine the diameter of the borehole, which determines what types of pumps can physically fit into it.
Select a specific model according to the delivery head, diameter, and required flow rate.
Consider additional components - sand separator, dry-run protection, check valve.

When is a surface pump suitable and when is a submersible pump clearly the better choice

Although this category focuses on submersible and borehole pumps for wells and boreholes, we often encounter the question at small depths of up to 7-8 m whether it is not simpler to use a surface pump placed, for example, in a technical room. Physically, the maximum theoretical suction height is limited by atmospheric pressure to approximately 10 m, but in practice, it is recommended not to exceed 6-7 m suction height with a surface pump, considering a margin of safety and losses. At greater depths, a submersible pump is clearly a more reliable and efficient choice, as it does not suffer from air intake problems and does not have to overcome a vacuum over a long suction line. A detailed comparison of the advantages and disadvantages of both types can be found in the article Submersible vs. Surface Pump for Water from a Well: What is More Cost-Effective.

Most frequently asked questions (FAQ)

How exactly do I determine the dynamic water level in my well?

The most reliable way is to do a test pumping - a measuring device (water level meter or even a simple rope with a weight) is lowered into the well and the drop in the water level is observed after several hours of pumping. For newly drilled wells, this value is usually provided by the drilling company in the drilling report. For older wells where the data is missing, we recommend an approximate measurement or consultation with a technician before purchasing a pump.

Can I use the same pump for supplying water to the house and for irrigating the garden?

In most cases, yes, if the pump is dimensioned with a sufficient flow reserve. However, you should consider that simultaneous irrigation and water use in the house may lead to a pressure drop. For larger gardens or irrigation systems with multiple sections, we recommend considering a pump with a higher flow rate, or solving the irrigation with a separate circuit and its own pressure tank.

What happens if I choose a pump with too low a delivery head?

The pump simply cannot pump the water to the desired location, or can only do so with minimal flow and low pressure. In practice, this means weak water pressure at the taps, problems with the water heater, which requires a minimum flow to start, or complete non-functionality when water is drawn from upper floors of the house.

What happens if I choose a pump with too high a power compared to the need?

An overly powerful pump is not only an unnecessary additional cost at the time of purchase and higher electricity consumption, but it can also cause practical problems - too fast pumping leads to a rapid drop in the dynamic water level (risk of dry running), increased wear due to frequent switching, and in some cases even excessive pressure in the distribution system, which must be addressed with a pressure-reducing valve.

Is there a difference between a borehole pump and a centrifugal pump in terms of price?

Borehole pumps for narrow boreholes are usually in a similar or slightly higher price range than centrifugal pumps with similar performance, especially at higher delivery heads, where the multi-stage borehole construction is more complex. The price difference is usually balanced by the fact that there is simply no alternative for a narrow borehole. A detailed comparison of specific models can be found in the article Comparison of Pumps STING and IBO – Which One to Choose.

Do I need to consider dry-run protection even for a shallow well?

We recommend it always, regardless of depth, because even in dug wells with a large water volume, the water level can drop significantly during dry summer months. Dry running of the pump, even for a short time, can cause permanent damage to the impeller or motor overheating, and this applies to all types of submersible and surface pumps.

Summary

Selecting the correct performance and delivery head of a pump according to the well depth is not just about one number - it is the sum of the actual depth and dynamic water level, the distance and elevation difference to the point of use, friction losses in the piping, and a safety margin for future changes. At small depths up to 8 m, you have a choice between a surface and a submersible solution. At medium depths of 15-30 m, centrifugal submersible pumps for 3" boreholes are most commonly used. At deeper and narrower boreholes, we move to STING type multi-stage borehole pumps, which can handle large delivery heads even in a limited diameter of 2". In case of any doubts about the calculation, we recommend consulting a technician before purchasing - an incorrectly dimensioned pump is one of the most expensive mistakes that is difficult and costly to fix later, especially if the pump is already installed deep in a narrow borehole.

Do you have a question on this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us - we are happy to help.