A surface pump sits above the water and pulls water through a suction line before pushing it onward. A submersible pump operates below the water and pushes water up the rising main. That simple placement changes priming, suction constraints, cooling, cable and retrieval, but it does not by itself decide efficiency or quality. The correct choice starts with the lowest expected pumping water level, source type, required flow and total dynamic head.
Why suction and discharge behave differently
A surface pump does not “lift by vacuum” without limits. Atmospheric pressure and losses constrain suction, and practical limits are below the theoretical maximum. Air leaks, warm water, altitude, excessive suction friction and low available submergence worsen performance and cavitation risk. The pump must be installed within its manufacturer’s suction boundary under the worst operating water level.
A submersible pump is surrounded by water and pushes upward. It avoids a long above-water suction lift but introduces underwater motor, cable, joints, riser pipe, non-return valve, protection and retrieval requirements. Correct submergence and cooling matter. Neither type can extract more sustainable water than the source supplies.
USGS explains that pumping a well lowers the local water level and can create a cone of depression. A static level of 5 m may become a pumping level of 10 m at the desired flow. A surface pump cited for 7 m suction would not become suitable because the static measurement looked shallow. Obtain a pumping test and seasonal evidence.
When a surface pump is a sensible candidate
Surface pumps can suit rivers, ponds, canals, tanks and genuinely shallow wells where the operating water level stays within the specified suction boundary. Access is usually convenient: the pump can be inspected, cleaned or moved without retrieving equipment from a borehole. Portable designs may serve changing plots or guarded storage.
The suction layout must still be engineered. Keep it short and adequately sized, minimize high points that trap air, seal every connection, use the specified foot valve or strainer and protect the intake from sediment and debris. Place the intake with enough water cover while keeping it away from the bottom. Flood, theft, livestock and unstable banks may make an apparently convenient location unsafe.
Futurepump’s official FAQ states a 7 m suction depth for its SE1 and SF2 surface solar pumps and a 15 m total-head limit. It says a shallow borehole can be considered where the water is less than 7 m below the surface. Treat that as a product-specific headline boundary. Confirm whether “water level” means the worst pumping condition for the proposed installation and obtain the flow curve at the complete duty.
When submersible is the practical route
A borehole whose pumping water level is too deep for surface suction generally requires a pump below water. Submersible pumps also suit installations where priming reliability and long suction lines would be problematic. The pump is hidden and quieter at the surface, but maintenance requires safe retrieval and adequate access.
Specify borehole internal diameter, total depth, casing and screen, static and pumping levels, tested yield, water quality, intended pump setting and any sediment risk. The pump must fit physically with cable and rising main. Controls should protect against dry running, overload, under/over-voltage and rapid cycling as appropriate. A level or flow sensor can prevent damage, but sensor placement and controller compatibility need design.
Water quality affects both pump types. Sand can erode pump components; iron, salinity or scaling can damage equipment and block irrigation. WRA lists water-quality analysis and borehole completion records among groundwater permit-stage requirements. A laboratory result also helps the equipment supplier select materials and filtration.
A decision matrix that avoids brand-first selection
| Question | Surface candidate | Submersible candidate |
|---|---|---|
| Operating water level | Within verified suction limit | Below practical suction reach |
| Source | Tank, pond, river, canal, shallow well | Borehole or deep well |
| Priming/air-leak risk | Must be managed | No long suction line |
| Routine access | Usually easy | Retrieval required |
| Underwater components | Intake/foot valve | Pump, motor, cable and joints |
| Main design evidence | Suction limit and pump curve | Borehole test, setting and pump curve |
This matrix does not say one type costs less. Compare complete installed systems at the same duty: pump, controller, panels, intake, riser/suction pipe, delivery pipe, tank, filters, civil works, protection, installation, retrieval equipment, spares, warranty process and energy availability. Then apply the petrol-versus-solar cash-flow method if the energy source is also changing.
Turn the choice into an installable brief
- Measure the source’s lowest credible operating level and tested sustainable yield.
- Calculate TDH at the required flow, including pressure and friction.
- Define water quality, sediment, intake protection and filtration.
- State pipe material, internal diameter, lengths, fittings and elevation profile.
- Plan dry-run, overflow and overcurrent protection plus safe isolation.
- Confirm mounting, security, flood exposure, livestock protection and maintenance access.
- Ask for the pump curve, array/controller limits, installation manual, warranty exclusions, local spares and service response.
For a surface-water abstraction, intake position and seasonal river or pond level can change both suction and environmental effects. For groundwater, WRA authorization and permitted abstraction do not disappear because the pump is solar. Measure flow and keep operation within the authorized volume.
Method and limitations
This guide is an exclusion and information-gathering method. It does not calculate net positive suction head, cavitation margin, motor cooling, cable voltage drop, pressure surge, pipe strength or borehole structural suitability. A qualified installer must use the actual manufacturer data and site survey.
Frequently asked questions
Can a surface pump draw from a borehole?
Only where the worst pumping water level remains within the verified practical suction limit and the intake, priming and sealing are correct. A “shallow borehole” label without pumping-level evidence is insufficient.
Is a submersible pump always more efficient?
No. Compare pump and motor efficiency at the actual duty point and include controller, cable and pipe losses. Position is not a guarantee of efficiency.