A single villa can treat water as a connection and a pump. A development of eight or twenty units cannot. Once several households draw from the same source in the same hours, water becomes infrastructure with a capacity, a failure mode and a maintenance owner, and it needs settling at the same stage as the access road and the drainage.
Peak demand, not average demand
The number that sizes a development's water system is not annual consumption. It is what happens between six and nine in the evening in high season, with most units occupied, showers running, and irrigation on a timer somebody set for the same window.
Averages hide that completely. A scheme sized on average daily use per villa will hold pressure in May and disappoint everyone in January. Occupancy pattern matters as much as unit count, because long stay rentals, short lets and owner occupied houses produce very different curves.
- Unit count, bedrooms, and realistic peak occupancy rather than average
- Pools, and whether they are filled once or topped up continuously
- Irrigated landscaping, which on a planted site often exceeds domestic use
- Shared facilities: gym, laundry, restaurant if there is one
- Phasing, because early units are occupied while later plots are still being built
One source is a single point of failure
Most schemes on Samui settle on a combination: a borehole, mains where it reaches, storage, and a delivery contract as the fallback. The right mix depends on the site. The principle does not. A development that can only be supplied one way will eventually be a development with no water, usually at the least convenient moment of the year.
On a larger site a second borehole is not always extravagance. Where the geology is uneven it provides redundancy, and it allows the scheme to alternate rather than over pump a single well.
Shared plant or plant per villa
This decision shapes how the scheme runs for its entire life, and it is far easier to make on paper than to change later.
Central plant, meaning one source, bulk storage and a distribution network, gives better economics, a single maintenance contract, and consistent water quality across every unit. It does require an owner after handover, which in practice means a management company or an owners' association with a budget and a contractor on call.
Per unit systems, where each villa has its own tanks, pump and filtration, push responsibility to individual owners and avoid the shared governance problem. They cost more in total equipment, make quality control harder, and tend to produce a patchwork of maintenance standards within a few years.
Hybrids work well in practice: a shared source and bulk storage, with per villa pressure sets and point of use treatment. Owners control their own pressure. The development controls the water.
Storage absorbs the mismatch
Sources deliver steadily. Developments consume in spikes. Storage is the buffer between those two facts, and on an island it is also the buffer against interruption, whether that is a supply cut, a failed pump, or a truck that cannot get up the access road in the rain.
Sizing bulk storage is a judgement about how long the scheme has to run unaided. That is a commercial decision as much as a technical one, and it belongs in the project brief rather than being left to whoever eventually specifies the tanks.
Pressure on a sloping site
Samui developments are frequently built up a hillside, which turns pressure into a design problem rather than a pump selection. A single pump set that satisfies the highest villa will over pressurise the lowest, wearing fittings and wasting water. Pressure zones, break tanks at intermediate levels and correctly placed reducing valves are the normal answers.
This is one of the areas where retrofitting genuinely hurts, because by the time the symptoms appear the pipe routes are buried under finished landscaping.
Construction needs its own water plan
Concrete, blockwork, cleaning and dust suppression consume a great deal of water, and they need it before the permanent system exists. Two approaches are common: drill early and run the build on the development's own borehole, or use delivered water through construction and commission the permanent system near completion.
Drilling early has an advantage beyond convenience. It converts the largest unknown in the whole water strategy, whether the site has a viable source and what it yields, into a known figure while the design can still respond to the answer.
Handover is part of the design
A water system handed over as a pile of installed equipment becomes an unmaintainable liability within a couple of years. What the eventual owners or managing agent need is a package: as built drawings of the network, the borehole log and test pumping report, pump and filtration specifications, water test results, a service schedule, and a plain statement of who maintains what.
Where units are sold individually that documentation also matters commercially. Buyers and their lawyers ask where the water comes from and who is responsible for it. A scheme that answers in writing presents materially better than one that cannot.
Developers, architects and project managers working on Samui, Phangan or Koh Tao are usually best served by fixing the water strategy alongside the site layout. Deep Well Samui can assess the source, size the system against real peak demand, and provide the specifications and documentation a scheme needs to be built and then maintained.