Monsoon rain and salt-water pools in Thailand: what heavy rain changes and how to manage it

What heavy rain changes in a salt-water pool and its plant

In heavy rain, water falling on the pool and the deck runs into the overflow channel and on into the balance tank. A tank with no overflow to waste or emergency drain fills and floods; low tank openings let garden runoff in; an underground pump room collects whatever drains towards it. Our projects include a flooded underground pump room, an overflow tank without an emergency drain and low tank openings admitting garden water.

A salt chlorinator generates sanitiser from the salt dissolved in the pool water. Rain and overflow losses dilute that salt, so the unit produces less and some units stop on a low-salt reading, just when leaves and runoff have raised the demand. Rainwater also lowers the water balance. The water is therefore tested on site after heavy rain and corrected from the results, not from a fixed schedule.

• Test water on site rather than assuming how rain has affected its balance
• Check skimmer baskets, pump baskets and filters as part of pool care
• Inspect tank openings and drainage where flooding or garden runoff has been reported
• Low tank openings let garden runoff in, while underground pump rooms risk damp and flooding

Managing water balance, salt chlorination and filtration

Filtration removes suspended debris; it does not disinfect. A salt chlorinator provides the disinfection by generating sanitiser from the salted water, and the water still has to be tested and balanced. In water chemistry there are no universal schedules or fixed product doses: source water, equipment, use and the finish all matter, and testing is done on site.

On our pool care contracts for villas, hotels and resorts, every visit follows a fixed checklist: skimming, brushing walls and steps, vacuuming the floor, emptying skimmer and pump baskets, backwashing the filter, and testing and balancing the water. For owners abroad, we send photo reports in a messaging group chat and log every water test.

An app-controlled smart controller can link the pump room to your phone, with a variable-speed pump, built-in salt chlorination and automatic dosing governed by live water sensors. When upgrading a pump room, we can keep a sound sand filter and refill it with PebblePure glass filter media.

• On-site water testing and balancing on every visit, with written or digital logs
• Variable-speed pumps running at lower flow for normal filtration and higher flow for backwashing
• Remote phone monitoring of water temperature, sanitiser levels and acid balance
• Checks of salt chlorinators, sand filters, automatic top-up valves and incoming water filtration vessels

Protecting the pump room and electrical controls from flooding

Flood protection options include moving vulnerable controls into weatherproof outdoor boxes and checking drainage pumps and emergency drains. At Five-Villa Lagoon Pool, we rebuilt a flooded underground pump room, moved rotted controls outside and fitted drainage pumps wired by water level. The inspection determines which changes suit another site.

We check emergency pump room drains and drainage pumps before the monsoon and on every care visit. Where a chamber is damp or flood-prone, we can move vulnerable control boxes into weatherproof outdoor enclosures, fit new drainage pumps started by a float switch with a high-water cut-out that switches the plant off if the water keeps rising, add an emergency drain and fit an air conditioner to keep the room dry. Drainage pumps need mains power, which can fail in the same storm, so an emergency drain that works without power matters wherever the levels allow one. At Private Residence, Laguna Park, we moved the pump room from the ground floor to the third floor. Moving a pump room up changes the hydraulics. The pump type, the pipe sizes, the non-return valves that stop the system draining back, and a floor drain in the new room are designed for the height, with you and your engineer — or, if you don't have one, with our partner engineer.

Converting to salt water and fitting a smart controller usually happens with the pool full by closing plant room isolation valves, though draining is sometimes necessary. Electrical work is agreed with the owner's electrician or engineer. Engineering decisions are made with you and your engineer — or, if you don't have one, with our partner engineer.

If a pump room has already flooded, do not go in and do not touch the equipment while the power is on. If the main board is dry and can be reached without stepping into water, switch the supply to the room off there; if not, keep away and call a licensed electrician. Before anything is restarted, a licensed electrician agreed with you checks the supply, the earthing and the earth-leakage protection. Thunderstorms also bring power cuts and surges; whether the controller and chlorinator need surge protection is a question for the same electrician.

• Moving control boxes out of damp underground chambers into weatherproof outdoor enclosures
• Fitting drainage pumps started by a float switch, with a high-water cut-out that switches the plant off if the water keeps rising
• Replacing worn valves and leaking filters at the same time, including automatic top-up valves that keep failing

Overflow channels, balance tanks and garden runoff

Flooding tanks and low openings admitting garden runoff need inspection before repairs are chosen. At Private Villa, Pasak — Alaska Ice, we added a forced emergency drain to an overflow tank that kept flooding.

A low-voltage bilge pump or any battery-backed pump has limited capacity. It is a last line of defence that protects the tank between visits, not the main drainage: a gravity overflow or a properly sized drainage pump does that work where the levels allow. The inspection decides what each tank needs.

At Private Villa, Rawai — Pearl White, the surge tank and water tank sat so deep that garden water ran into them; we raised both openings and cast new concrete lids. At Private Villa, Rawai — Polar White, an overflow rendered level with the terrace let water escape under the terrace and house; we stopped it by rebuilding the overflow slightly lower, and recast the drain channel with a new grating.

We inspect concrete tank walls, floors, corners and pipe entries before choosing repairs. Tanks must be emptied and dried before waterproofing, which is hardest in the wet season: groundwater can press in through the walls of an empty below-ground tank and stop it drying, so the timing is planned around the season and the groundwater level, with you and your engineer — or, if you don't have one, with our partner engineer. Rigid cementitious systems suit bases that do not move; negative-side waterproofing addresses groundwater pressing in from outside. A tank-in-tank rebuild may suit an old tank too damaged for direct repair. Not every hidden problem can be seen at once, so testing and restarting after repairs may go in stages.

• Adding a forced emergency drain to an overflow tank that floods
• Raising low surge and storage tank openings and casting new concrete lids
• Waterproofing emptied and dried concrete tanks, including negative-side waterproofing below ground

Looking after a pool while you are away in the rainy season

Agree whether the pool should remain in water with reduced circulation and checks, or be drained and conserved. The choice depends on its structure, finish, equipment, nearby trees and groundwater conditions. Covers or rented roofs and tents are options where the site allows, with checks during visits.

Many pools are best kept running at low effort with reduced circulation, balanced water and periodic checks. Draining is the option that needs most care in the monsoon: the groundwater is then at its highest, an empty shell can be lifted or cracked by its pressure, and some finishes do not suit standing dry in the sun. We check the site and the groundwater before recommending it. We can fit a pool cover or, where the site allows, rent a roof or tent over the pool, and check the cover, pool and pump room drainage pumps on every visit. Before you return, we bring the pool back into service; tell us in advance if refilling from a borehole, lake or river, as that water can stain the finish.

• Keeping the pool running at low effort or draining and conserving it where groundwater and finish allow
• Fitting a pool cover or renting a roof or tent over the pool, checked on every visit

What to send us for a first discussion

Send photos of the pool, overflow edge, tank access and pump room, with your location and approximate pool length, width and depth. Say whether the pump room is underground and describe any flooding or damp. Tell us whether you need water care, equipment changes, tank repairs or care while away.

• Photos of the pool, the overflow edge, the surge or balance tank access and the pump room
• Your location in Phuket or elsewhere in Thailand and the approximate pool length, width and depth
• Whether the pump room is underground, any signs of flooding, and what help you need

Further reading

• Salt chlorinators and cement-based pool finishes