Drilling
Two quotes for the same villa can be far apart and both be honest. The gap is almost always in what each one includes, and that is something you can check line by line before you sign.
October 1, 2026 · 8 min read
A deep well drilling quote is easy to misread. One contractor sends a single figure for 'drilling', another sends two pages covering casing, testing, a named pump and the pipe to your tank, and the first one looks like the bargain. It often isn't, because the two documents describe different end results: a cased hole in the ground in one case, water arriving at your taps in the other. This guide walks through what a complete quotation for a villa well on Koh Samui should cover, why prices between neighbouring plots differ so much, and the questions that make two quotes comparable.
We don't publish a price list here, and we'd be wary of anyone who quotes a firm figure for an island well without seeing the plot. What we can show is what goes into the number, so you can tell whether a quote covers it.
Picture two projects a short drive apart. The first is a house on the flat behind Maenam: a wide concrete driveway, soft weathered ground, a modest household demand and mains water as a fallback. The second is a five-bedroom pool villa on the hillside above Chaweng Noi: a steep, narrow soi, granite close to the surface, a garden to irrigate through the dry season, and the well expected to carry the whole property. Both owners ask for 'a well'. The second project needs a smaller rig or extra site preparation, likely more depth through harder rock, a stronger pump hung deeper, and more storage and pressure equipment at the top. Its quote will be higher, and it should be.
Depth, rock, access and casing are the main drivers, and they have their own article: what drives the cost of a well on Koh Samui. The rest of this page is about the paperwork: what a quote should spell out so you can see how those drivers were priced.
Anatomy of a quotation
The eight parts of a villa well that a full quotation prices. Each one moves with the conditions listed under it.
01
Getting the rig and compressor to the drilling point and set up level, including any site preparation.
Price moves with
02
The bore itself, usually priced per metre against an expected depth range, or as a total with a stated depth.
Price moves with
03
The lining that keeps the bore open, the screened section that lets water in, and the seal that keeps surface water out.
Price moves with
04
Clearing drilling fines from the bore, then pumping at a steady rate to measure yield and drawdown.
Price moves with
05
A named pump model sized to the measured yield, hung at a stated depth on riser pipe with drop cable and safety rope.
Price moves with
06
Control box, dry-run and surge protection, and the cable run back to the property's electrical board.
Price moves with
07
The line from wellhead to tank, the storage tank itself, and the pressure tank or booster set that feeds the house.
Price moves with
08
A laboratory analysis of the new well, and treatment designed from its results if the water needs any.
Price moves with
Most island wells are quoted against an expected depth range, because nobody can see the fractures in the granite before drilling (our guide to well depths on Koh Samui explains why). A per-metre rate is transparent as long as the quote also states the expected range and what happens beyond it. A single total is fine too, provided it names the depth it covers. The quote to question is the one that says neither.
Casing is the part of the well you can't upgrade later without starting again, and it is the classic place for a low price to come from. A useful quote names the material, the diameter and roughly how much of the bore will be cased, plus how the top is sealed against surface water. A larger diameter costs more but leaves room for a bigger pump if demand grows. What casing, screen and seal actually do underground is explained in inside a deep well.
A bore that has not been developed sends fine sediment into the house and wears out its first pump. A bore that has not been test-pumped leaves the pump size to guesswork. Both cost time on site, and both are easy to leave off a quote to make it shorter. You want development included, a test of stated length, and yield and drawdown recorded in writing.
'Pump included' tells you nothing about size, materials or how long it will last. A complete quote names the model and the setting depth, and the sizing should follow from the yield test rather than precede it. Some contractors quote the pump as provisional for that reason, which is honest. Our guide to choosing a submersible deep-well pump covers what the sizing should be based on.
Trenching, pipe to the tank, the tank, and the pressure equipment that feeds the taps are often quoted separately or by another trade. That is fine, as long as you know who is doing it. When nobody quotes the connection, the well is finished and the house still has no water. Tank sizing and pressure have their own guides on storage tank size and pressure tanks.
| Drilling-only quote | Complete system quote | |
|---|---|---|
| What you have at the end | A cased hole | Water at the taps, with figures on paper |
| Casing and seal | Sometimes unspecified | Material, diameter, depth and seal stated |
| Development and yield test | Often missing | Included, with yield and drawdown recorded |
| Pump and controls | Separate purchase | Named model, setting depth, protection |
| Connection to tank and pressure | Another trade | Included or clearly excluded |
| Water test | Rarely | Included, with treatment advised from the results |
| If the system underperforms | Each trade points at the next | One contractor owns the result |
A drilling-only price isn't dishonest. It just answers a different question. The missing lines come back later as separate purchases, often bought in a hurry, sized without test data, and installed by someone who never saw the well being drilled. Compare quotes on what you have at the end of each, not on the first number you see.
You'll get a far better first estimate, and a shorter survey visit, if you send these with your enquiry:
Question 6 matters most. Groundwater on the island sits in fractures, not in a lake, and even a careful survey reduces the risk of a poor well without removing it. A contractor who explains in writing what happens in that case, whether that means drilling deeper within an agreed limit, moving to a second spot or a reduced charge, is one you can plan around.
Planning a new well? Send us your location and project details for an assessment: a few photos of the access and a note on what the water is for are enough to start. After a site survey we provide a fixed, itemised quotation for deep well drilling and everything up to the tank, with each line above either priced or clearly excluded.
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
Equipment
Horsepower is the last number to look at. A pump is matched to what the well can give and what the property needs, and both sides can be measured.
August 27, 2026 · 6 min read
Drilling
"The pump gave 40 litres a minute" sounds like an answer, but it describes the pump on one afternoon, not what the well can keep giving. Yield is read from the water level: how far it falls while pumping, whether it settles, and how it comes back afterwards.
July 10, 2026 · 9 min read