23 hours ago, turgid said:

If the PVC pipe is properly sealed water can only enter at the bottom of the Well. 

Everything else is accurate for domestic pumps. As to water ingress usually the bottom couple of metres or last 4 metre section is slotted at regular intervals with an angle grinder. You can buy preslotted pipe in a few hardware shops in Thailand but DIY is more common. 

On 2/1/2019 at 10:39 PM, turgid said:

In our case the water is coming from 40 Metres deep and if left alone today will  rise to 7 Metres below ground level in the well.

So if you shove a pipe down the well and pump.

 

Watch out for that, because during the dry season when the nearby farmers are pumping to beat the band, that standing water level may drop significantly.  Depending on the well inflow performance and the amount you want to pump, the dynamic fluid level may also drop quite a bit while you're pulling on it.

 

The only downside to setting the pump just above the water zone is a little extra pipe (and cable if it's an ESP), along with a minuscule increase in friction losses, assuming the tubing is adequately sized.  Total dynamic head (TDH) is calculated by net lift (that 7 meters you mentioned) + friction losses pumping through the pipe + wellhead pressure.  The only factor that changes if you set the pump intake deeper is the friction loss, and that's tiny over 40 meters (again, assuming properly sized down pipe)  

 

You'll also need more, and possibly bigger cable if you use a deep-set electric submersible pump (ESP) since there will be a voltage drop on the additional cable, but refer to the Franklin AIS for proper cable sizing if you're running an ESP.  If it's a surface set "deep well pump", there will be no additional cable.

 

You'll have to Google the Franklin AIS for 50 Hz applications.  Well worth the effort for anyone wanting to understand ESP's for water wells.'