I have a 4" borehole, 20m deep at my house that i want to use as a backup for the mains supply which is very unreliable. Is a surface mounted pump okay for this or do i need a submersible? The primary use will be for watering the garden.

Thanks, suart04

At 20m deep a surface pump will work just fine . This is what I have and have had no problem.

If the Pumping level is less than 6-7 meters below the surface,

then a cheap centrifugal is a good option.

If the pumping level is deeper than around 6-7 meters,

a surface centrifugal will not pull the water up.

It is all based on Atmospheric Pressure,

One Atmosphere =10.35 meters of Water.

A pump will not pull the full 10.35 meters,

because there is efficiency loss in the pump,

and friction loss in the suction pipe and the foot valve.

A submersible doesn't have this concern,

as the impellers are below the water surface.

It comes then to a cost consideration,

initial cost versus ongoing energy costs.

Recently there was a post about jet pump,

which is a reasonable solution

if the pumping level is deeper than 6 meters

by means of it's low initial cost,

if only a small volume of water is needed.

Jet Pump efficiency is only about 40%,

versus a cheap centrifugal about 70%,

and a high quality pump up to 85%.

Since centrifugals are expensive,

and therefore should be more efficient

it is safe to calculate will have half the energy cost of a jet pump.

The best way to precisely describe the comparison is with a spreadsheet calculator

In order to change the yellow box parameters,

you may need to save to file and open from there.

Energy_Consumption_Comparison_of_Pump_Types_20100406.xls

Edited April 6, 201016 yr by WatersEdge

If you have 4 inch casing in well and the well provides adequate volume, you can run 2 inch pipe with a check valve (this will keep fluid level at/near surface) and use 2 inch self priming, centrifugal surface pump. This should give plenty of volume for a garden area around your house. Pumps have discharge rate at specific rpm stamped on pump plate. Its just a matter of matching power source to pump.

At 20m deep a surface pump will work just fine . This is what I have and have had no problem.

you seem to have a "jet pump". a normal suction pump with a single pipe/hose cannot draw a single drop of water from that depth.

The op's mention of a 20meter deep well bore and subsequent questions could gain some real input if he will tell us the depth to the water source in his well bore, the volume it will produce, as tested, when drilled, and the volume he wants to pump. As naam mentioned a normal suction pump with 20 meter fluid level will not work. Now if the water column in a 20 meter well stands at 2 meter from surface, thats a different ball game.

The op's mention of a 20meter deep well bore and subsequent questions could gain some real input if he will tell us the depth to the water source in his well bore, the volume it will produce, as tested, when drilled, and the volume he wants to pump. As naam mentioned a normal suction pump with 20 meter fluid level will not work. Now if the water column in a 20 meter well stands at 2 meter from surface, thats a different ball game.

good that you mentioned that Slapout. i recently visited a friend in Chiang Mai who told me that he is pumping water from 31 meter depth with a normal suction pump. when i told him that the laws of physics apply in Chiang Mai too he was quite pissed off and showed me his setup. as the 4" pipe was not covered we measured the water level with a soft drink bottle on a thread. result: water level less than 3 meters below surface

The op's mention of a 20meter deep well bore and subsequent questions could gain some real input if he will tell us the depth to the water source in his well bore, the volume it will produce, as tested, when drilled, and the volume he wants to pump. As naam mentioned a normal suction pump with 20 meter fluid level will not work. Now if the water column in a 20 meter well stands at 2 meter from surface, thats a different ball game.

The borehole is not yet complete, the bossman is not here, and as i write this his 3 labourers are lying under a tree in my garden. When i have more details for you i will report back. It is only intended for watering my small garden, maybe washing the car and topping up my household tank when the mains supply is off. It would be nice to have it up and running by Songkran, so me and the kids can give the neighbours a soaking!