Domakihub How to Drain and Refill a Pool Safely and Correctly
A practical step-by-step guide for homeowners, villa owners, and hospitality managers in Greece.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
Draining and refilling a pool is one of the most demanding maintenance tasks you will face as a pool owner, but it is sometimes unavoidable — whether you are dealing with an unrecoverable chemical imbalance, stubborn algae, or a liner repair. The video above walks through the full process visually, while this guide breaks it into clear, actionable steps suited to the conditions you will encounter in Greece, from private villas on the islands to rooftop pools in Athens hotels. Get the timing, equipment, and rebalancing steps right and you will protect both your pool shell and your water quality from day one.
When Should You Actually Drain Your Pool?
Complete drainage is a last resort, not routine maintenance. In most cases — cloudy water, high chlorine demand, a modest algae outbreak — shock treatment, clarifiers, and a good backwash cycle will fix the problem without removing a single litre of water. Reserve a full drain for situations where total dissolved solids (TDS) exceed roughly 3,000 ppm, where cyanuric acid has built up beyond 100 ppm and cannot be diluted, where you need to resurface or repair the shell, or where a black algae infestation has penetrated plaster and brushing alone will not reach it.
In Greek summer conditions, with intense UV exposure and heavy bather loads in holiday rentals and hotels, TDS can climb faster than in temperate climates — so annual water testing is worth adding to your maintenance calendar, even if you hope to avoid a drain.
Key Risks to Know Before You Start
Hydrostatic pressure is the biggest structural risk for inground pools. When the water that normally counterbalances groundwater pressure is removed, rising groundwater can crack or pop an empty concrete or fibreglass shell, particularly in areas with a high water table or after heavy rain. Always check local groundwater conditions and, if in doubt, consult a pool technician before emptying a gunite or fibreglass pool. Vinyl-liner pools carry a different risk: without water weight keeping it seated, the liner can shrink, wrinkle, or tear, so a vinyl pool should never sit empty longer than absolutely necessary.
Drainage water may not flow legally into the street or storm drains in Greek municipalities without permission, since pool water contains chlorine and other chemicals. Check local regulations, or discharge slowly into a municipal sewer connection where permitted.
How to Drain and Refill Your Pool: 5 Steps
- 1
Stop adding chemicals and run the pump down
At least 24 hours before you start draining, stop adding any chemicals and let the pump circulate to help consume residual chlorine. The lower the chlorine level in the drained water, the better it is for the environment. Turn off the pool heater and any salt chlorinator to protect those units from running dry.
- 2
Set up a submersible pump and direct the discharge
Attach a submersible or sump pump to a discharge hose long enough to reach a suitable drain point — ideally a sewer cleanout or a large landscaped area that can absorb the volume gradually. Lower the pump to the deepest point of the pool (usually the main drain end), start it, and monitor the flow. A standard 1.5 HP submersible pump will empty a 50,000-litre pool in roughly eight to twelve hours. Check on it every hour to clear debris and ensure the hose has not kinked or shifted.
- 3
Clean the shell while it is empty
Once the pool is empty, work quickly. Scrub the walls and floor with a pool brush and a mild acid wash or tile cleaner to remove calcium scale, algae staining, and biofilm. Rinse thoroughly with fresh water and let it drain through the main drain or pump out the rinse water. If you are doing structural repairs — replastering, patching cracks, replacing tiles — this is the window to complete that work. In summer heat, an empty concrete shell can overheat and surface damage can occur within hours, so shade the pool or begin refilling the same day if no repairs are needed.
- 4
Start refilling immediately and monitor the water level
Begin filling with a standard garden hose connected to your mains supply, or arrange a tanker delivery for large pools if mains pressure is too slow. Place the hose at the shallow end or over the main drain area to prevent air locks. Never leave the fill unattended for long stretches — an overflowing pool on a tiled terrace creates a slip hazard and wastes significant water. A 50,000-litre pool on typical Greek mains pressure (around 3 to 5 bar) will fill in ten to sixteen hours depending on hose diameter and supply pressure.
- 5
Rebalance the water chemistry before swimming
Once the water reaches the middle of the skimmer opening, start the circulation pump and begin chemical balancing. Work in the following order: first adjust pH to 7.2–7.6, then total alkalinity to 80–120 ppm, then calcium hardness to 200–400 ppm, and finally add a chlorine shock dose to build an initial sanitiser residue. Allow at least 24 hours of filtration and re-test before anyone swims. If you are on a saltwater system, add the salt dose for your pool volume and run the chlorinator only once the salt level has reached the manufacturer's target range.
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FAQ
- How often does a pool need to be completely drained?
- Most well-maintained pools in Greece will go three to five years between full drains. Regular partial water changes (replacing 10–15% of the volume every season), consistent chemical management, and annual TDS testing are usually enough to avoid a full drainage. Pools with heavy bather loads — holiday rentals, hotel pools — may need to drain sooner if TDS climbs rapidly.
- Can I drain my pool into the street or the garden?
- Not without precautions. Pool water contains chlorine, algaecides, and other chemicals that can harm plants, fish, and soil organisms. Allow free chlorine to drop below 0.1 ppm before discharging, and never direct pool water into a storm drain or waterway. In Greek municipalities, check whether a sewer connection is available and permitted for this use — many local councils require it.
- How long can I leave my concrete pool empty?
- As short a time as possible — ideally no more than two to four days in summer. An empty concrete shell is vulnerable to hydrostatic pressure from groundwater, thermal expansion, and surface cracking in intense heat. If you anticipate delays (waiting for a resurfacing crew, for example), consult a structural pool technician about whether to partially refill the pool to relieve pressure while you wait.