A private well is not the right answer for every property on Samui. For a lot of them it is the difference between a house that runs normally through April and one that spends the dry months waiting on a delivery truck. Before committing to a borehole it helps to know what the work involves, what can be predicted in advance, and what genuinely cannot.
When a private well is worth costing out
The clearest cases are properties with steady year round demand that the mains supply struggles to meet: villas with a pool and planted garden, small resorts, and houses on higher ground where line pressure falls away. Irrigation is often the deciding factor. A garden watered daily through the dry season quietly uses more water than the people living there.
It makes less sense on a small plot with modest demand and a connection that has never given trouble. Drilling has a cost floor, and if the water it replaces is cheap and dependable, the payback period stretches out a long way.
- Mains pressure that drops in the afternoon or through high season
- Repeat top ups from delivery trucks, particularly February to May
- A pool, irrigated garden, or several bathrooms in the plan
- A hillside plot where the supply line arrives with little pressure left
- A build or renovation with the trenches already open
The survey decides more than the price
Everything downstream depends on this visit. A survey reads the terrain, the elevation, the position of the plot relative to the island's granite core, and whatever is known about wells nearby. Out of that comes an expected depth range and a drilling plan, which is as close to a prediction as anyone can honestly offer before the drill turns.
Access is the part owners tend to underestimate. Rigs are heavy machines. Narrow sois, steep driveways, soft ground after rain, low cables and tight corners all decide which rig can be used, where it can stand, and how long setup takes. Finding an access problem on foot costs nothing. Finding it on the morning the rig is booked costs a day.
Results from the plot next door are useful evidence, not a guarantee. Fracture patterns in granite change over short distances, which is why two neighbours can end up with different depths and different yields.
What happens on site
The first part of the day goes on positioning and levelling the rig and setting up for the water and cuttings that come back to the surface. Drilling then runs in stages, and the crew logs what the ground returns as it goes. Changes in the cuttings and in the rate of penetration are the first real information anyone has about the formation under the plot.
How long it takes depends on depth and on rock. Weathered material drills quickly. Solid granite is slow, patient work. A range is the honest answer to the question of how many days, at least until the hole is actually started.
Casing and development
The bore is lined with casing so it cannot collapse, and to seal off layers that should not be feeding the well. Screened sections sit against the water bearing zones so water enters where it is supposed to. This is the part of a well that cannot be corrected cheaply later, and it is the usual place to find corners cut behind an unusually low quote.
Once the casing is in, the well is developed: pumped and surged to pull the drilling fines out of the formation around the screen. Skipping development is why some new wells produce cloudy water for months and wear out their first pump early.
Test pumping turns a hole into a water supply
A bore full of water is not yet a supply. Test pumping measures what the well sustains over a period of continuous running, and how far the water level falls while it runs. Those two figures, yield and drawdown, are what a pump is specified against. A report that gives yield without drawdown is showing half the picture.
Specifying the pump
Submersible pumps are matched to three things: what the well sustains, the depth the pump will hang at, and the pressure the property needs at the far end. Oversizing is the common and expensive mistake. A pump that can draw more than the well gives will pull the level down to its intake, run dry, cycle, and fail early.
Setting depth follows from the drawdown measured during testing, with margin below it. It is not a matter of lowering the pump towards the bottom of the bore and hoping.
Water quality is a separate question
Quantity and quality are unrelated. A strong well can produce water that stains every fitting in the house. Island groundwater commonly carries hardness, iron and manganese, at levels that vary from bore to bore, so treatment is sized from a water test rather than from a general assumption about the area.
After the well is handed over
A well is a mechanical system with a service life. Pumps wear, filter media loads up, pressure vessels lose their charge. Most of the failures that leave a property dry in high season announce themselves months earlier through small changes in pressure, noise, or how often the pump starts.
Anyone weighing up a well on Samui gets further with a site assessment than with a phone quote. Deep Well Samui can walk the plot, give an expected depth range and an access plan, and specify the drilling, pump and treatment the property actually needs.