Water Supply
A well is not better or worse than mains water in general. It is worth drilling when it solves a real problem for this property, at a cost and with responsibilities the owner accepts. Six questions decide it: what mains water is available, how much the property needs, how much reliability matters, whether a well can be drilled here, what the water will need, and who will look after it.
June 28, 2026 · 9 min read
Owners usually frame this as a comparison: which is cheaper, which is cleaner, which is more reliable. In practice the answer depends far more on the property than on the sources. A small house on a road with a dependable connection and a large rental villa with a pool, a planted garden and no mains nearby are asking different questions. What follows is a way to work through the decision for one property, before anyone quotes for drilling.
The first question is not about the well at all. It is whether the plot has a usable alternative, and how good it is. General impressions of mains supply on the island are not much help here, because experience varies from one road to the next. What matters is this connection, at this plot.
The size and pattern of demand change the answer more than anything else. A couple living quietly use a fraction of what a full rental villa uses in high season, and a pool or a large irrigated garden can outweigh everything used indoors. Demand that peaks in the dry months is the hardest to supply from any single source.
For irrigation in particular, see garden irrigation from a well, which covers when a well is a good source for the garden and when it is not.
A well does not have to replace mains water to be worth having. It can be the main source with mains as the fallback, the fallback behind mains, or a source for a single use such as the garden. The question is how much a day without water would cost. For an owner-occupied home, an occasional interruption with a decent reserve in the tank may be acceptable. For a rental villa, a dry day can mean refunds and reviews, and two independent sources start to look like insurance.
If the answer is both, the two sources should meet in the storage tank, each with its own protected inlet, with level control deciding which refills first. How to arrange that is the subject of running a well alongside mains water.
A well only makes sense if the site allows one. Three things have to line up: physical access, a suitable position, and ground that gives water.
Cost follows from these same factors, chiefly depth, access and what has to be installed after the hole. What affects the cost of drilling a well breaks that down.
Groundwater on the island varies from bore to bore. Some wells give water that needs little more than sediment filtration; others need iron and manganese removal, softening, disinfection or a salinity check. Mains water has its own path to the tap, usually through the property's storage tank, which has to be kept clean. The only fair comparison is a laboratory test of the well water once it exists, and a treatment budget that follows from it. Until then, assume some treatment may be needed for drinking water. See testing well water before choosing treatment.
A well is equipment the owner is responsible for. Choosing mains does not remove every responsibility either. The table sets out who looks after what in each case.
| With a private well | With mains water only | |
|---|---|---|
| Source equipment | Submersible pump, cable, controls and protection, replaced or repaired over the years | The connection up to the meter is not the owner's equipment |
| Power | The pump needs electricity, and stops in a power cut unless backed up | None for the supply itself |
| Water quality | Testing, and treatment where the test calls for it, with its own servicing | Keeping the storage tank clean; treatment only if wanted |
| Storage and pressure | Tank, pressure pump and controls | Usually the same: tank, pressure pump and controls |
| When supply stops | A fault the owner arranges to have fixed | An interruption the owner waits out on stored water |
Sometimes, but often not. Whether a well costs less per cubic metre than mains depends on the drilling cost, the pump's energy use, treatment, maintenance and the local tariff, and those differ from property to property. Many owners who drill are buying reliability and control rather than cheaper water. If cost is the main reason, it deserves real figures for this site, not a general rule.
Decision aid
A way to organise the decision, not an engineering calculation. Each answer points in a direction; the site survey and the figures settle it.
Judged from this connection and its history, not from general reports.
A pool, a large garden, many bathrooms, or a rental villa that fills up in the dry months.
Guests, staff, a business, or an owner who is often away.
Clear of septic systems and drainage, with open space above for lifting the pump later.
A laboratory test, treatment where it is needed, and a pump that needs servicing.
Likely direction
Dependable mains, modest demand, and an owner who prefers not to run equipment.
No dependable mains, a site that can be drilled, and an owner ready to maintain it.
Mains available, but demand or the cost of a dry day justifies a second source.
The decision is quicker with a few facts to hand: the plot's location and access, whether mains water reaches it and how it has behaved, the planned or current occupancy, and whether there is a pool or a large garden. If a well already exists on a neighbouring plot, anything known about its depth or water helps too.
Not sure whether this property needs its own well? Send the location and planned water demand so we can review the options. See deep well drilling and villa water systems, or send the details.
Water Supply
Plenty of villas on Koh Samui have a well and a mains connection. The question is not which one to keep — it is how to connect two sources so they back each other up without fighting, without contaminating anything, and without anyone having to be home to switch valves.
October 19, 2026 · 10 min read
Drilling
There is no honest average price for a villa well on the island, because the bill is built from parts that change plot by plot. This guide takes the cost apart: which parts are fixed, which grow with every metre, which can only be confirmed once the bore is going down, and which of them you can influence before the rig arrives.
July 1, 2026 · 9 min read
Drilling
The drilling is the crew's job. Getting the rig to the right spot, keeping the garden and the neighbours on side, and knowing which decisions will come to you during the work all go better when the owner knows what's coming.
October 1, 2026 · 10 min read