How Long Does a Pool Drain and Refill Take? (Honest Timelines for Fresno Homeowners)
By Nancy Padjan | 7 min read
If you're facing a pool drain and refill, one of the first questions you're probably asking is: how long is this actually going to take? The honest answer is that it depends on several variables specific to your pool and your situation, but for most Fresno homeowners, you're looking at a total process of two to four days from start to swim-ready.
That timeline breaks down into distinct phases: draining, cleaning and any surface treatment, refilling, and chemical startup. Each phase has its own timeline and its own risks, and in Fresno's climate, the risks of getting the timing wrong are higher than in more temperate parts of California.
Here's a clear, realistic breakdown of the entire process.
Phase 1: Draining the Pool
How long it takes
Draining a residential pool takes between 8 and 14 hours depending on pool size and the draining method used.
The most common approach is to use a submersible sump pump positioned in the deep end of the pool. A quality submersible pump moves roughly 30 to 50 gallons per minute depending on its rating. At that rate:
A 15,000-gallon pool drains in approximately 5 to 8 hours
A 20,000-gallon pool drains in approximately 7 to 11 hours
A 25,000-gallon pool drains in approximately 8 to 14 hours
Using your pool's filter system on waste mode is another option but it is slower and only effective down to the skimmer line. For a complete drain, a submersible pump is the right tool.
What happens to the water
Before draining, the water should be dechlorinated by stopping chemical additions and allowing chlorine to dissipate naturally, or by adding a neutralizer. Fresno's municipal code requires pool water to be directed to the sanitary sewer system rather than storm drains or the street. The cleanout access point for your home's sewer line is the standard discharge point. A professional pool service technician will handle this correctly.
The critical timing issue: do not drain during peak summer heat
This is where Fresno's climate creates a genuine complication. Empty pool shells are vulnerable, and the summer sun here is not forgiving.
Direct sun on exposed plaster at 105 degrees can cause the surface to dry, blister, and crack within hours. Fiberglass shells can delaminate. The goal is to drain, complete the work, and begin refilling as quickly as possible. For a standard drain and restart, the pool should never sit empty overnight in Fresno's summer heat if it can be avoided.
The safest time to drain a Fresno pool is early morning when temperatures are lower and you have the maximum number of daylight hours to complete the work and begin refilling before nightfall.
Phase 2: Cleaning and Surface Treatment
Standard clean (no acid wash)
If you are draining simply to reset chemistry, the shell cleaning is straightforward: pressure washing the walls and floor, scrubbing any scale or algae residue, and clearing drains and fittings. This typically takes 2 to 4 hours for a residential pool.
Acid wash
An acid wash is a more intensive surface treatment used when plaster has significant staining, deep-set algae, or calcium silicate deposits that cannot be treated chemically with water in the pool. The process involves applying a diluted muriatic acid solution to the pool surface, scrubbing, and rinsing, working methodically from the top of the walls down to the floor drain.
A professional acid wash on a residential pool takes 4 to 8 hours depending on pool size and the condition of the surface. The acid solution must be carefully neutralized before it enters the sewer.
An acid wash removes a thin layer of plaster each time it is performed. For this reason, it should not be done routinely. Most plaster pools can tolerate three to five acid washes over their lifetime before replastering is required.
Chlorine wash
A chlorine wash uses a high-concentration sodium hypochlorite solution rather than acid. It is effective for severe algae infestations, particularly black algae, and is less aggressive on the plaster surface than an acid wash. It is not as effective for calcium scale or deep staining. A chlorine wash takes a similar amount of time to an acid wash.
Phase 3: Refilling the Pool
How long it takes
Refilling is the most time-consuming phase of the process and the one most people underestimate.
A standard residential garden hose flows at roughly 8 to 10 gallons per minute, or about 500 to 600 gallons per hour. At that rate:
A 15,000-gallon pool takes approximately 25 to 30 hours to refill
A 20,000-gallon pool takes approximately 33 to 40 hours to refill
A 25,000-gallon pool takes approximately 42 to 50 hours to refill
In practical terms: most Fresno residential pools take between 24 and 48 hours to refill with a garden hose. Larger pools at the higher end of residential sizes can take close to two full days.
You can reduce refill time by using two hoses running simultaneously, or by using a larger diameter hose which increases flow rate. Professional services can also arrange for accelerated fill methods in some cases.
Do not leave the pool unattended while refilling
An overflowing pool is a significant problem. The structural and water damage from overflow can be substantial, and the wasted water in Fresno's water-scarce environment is worth taking seriously. Stay on property and check water levels regularly throughout the refill. Set a timer to remind yourself every hour.
Fresno water cost consideration
At Fresno's residential water rates, refilling a 20,000-gallon pool will cost approximately $100 to $200 in water charges depending on your rate tier and time of year. This is worth factoring into your decision-making. A partial drain and refill (replacing 30 to 50 percent of the water rather than all of it) costs proportionally less and can be an effective approach when calcium hardness is elevated but not severely so.
The waterline tile problem during refill
As your pool refills, the waterline tile is going to show you clearly how much calcium is in your fill water. Fresno tap water is among the hardest in California, meaning every gallon you add brings significant dissolved calcium into the system. This is why a drain and restart in Fresno is not a permanent solution to calcium hardness. It resets the clock, but the calcium starts accumulating again immediately from day one of refill.
Phase 4: Chemical Startup
How long it takes
Getting newly filled water properly balanced and ready to swim takes 24 to 48 hours from the time refilling is complete.
Fresh water from the tap does not equal safe swimming water. Fresno's tap water arrives with its own chemistry that needs adjustment before the pool is swimmer-ready. After refilling, a professional startup includes:
Full water test covering pH, alkalinity, calcium hardness, chlorine, and stabilizer
Adjustment of alkalinity first, then pH
Chlorine and stabilizer addition
Filter run for a minimum of 24 hours to fully circulate and distribute chemicals
Follow-up test to confirm all parameters are in range
In some cases, calcium hardness and TDS in Fresno tap water are already elevated enough that the startup chemistry presents challenges from the first fill. A good pool service technician will test and communicate this clearly rather than letting you discover it weeks later.
When is the pool safe to swim?
The pool is ready to swim when:
pH is between 7.2 and 7.6
Free chlorine is between 1.0 and 3.0 ppm
Alkalinity is between 80 and 120 ppm
Calcium hardness is between 200 and 400 ppm
Water is visually clear
Do not rush this phase. Swimming in improperly balanced fresh water causes eye and skin irritation and can damage pool surfaces and equipment.
The Full Timeline: Start to Swim-Ready
Putting it all together, here is a realistic timeline for a professional drain and restart in Fresno:
| Phase | Typical Duration |
|---|---|
| Draining | 8 to 14 hours |
| Cleaning (standard) | 2 to 4 hours |
| Acid or chlorine wash (if needed) | 4 to 8 hours |
| Refilling | 24 to 48 hours |
| Chemical startup and circulation | 24 to 48 hours |
| Total start to swim-ready | 2 to 4 days |
For a standard drain and restart without acid wash, two to three days is a realistic expectation. With an acid wash, plan for three to four days. These timelines assume work begins early in the morning on day one and that refilling runs continuously.
Why Fresno Pools Need Drains More Frequently Than Average
The national recommendation for pool drains is every five to seven years for well-maintained pools. In Fresno, that interval is often shorter.
The reason comes back to hard water. Fresno draws its water supply from underground aquifers that carry significantly elevated levels of dissolved calcium and magnesium. Total dissolved solids in Fresno tap water run nearly double the national average. Every gallon you add to top off evaporation, every inch of water lost to Fresno's hot summers, leaves more calcium concentrated in the water.
When calcium hardness climbs above 500 to 600 ppm, no amount of chemical management fully compensates. Scale forms on surfaces and equipment. Water chemistry becomes increasingly difficult to balance. Chlorine works less efficiently. The only real solution at that point is dilution, which means a partial or full drain and refill.
Many Fresno pool owners who maintain consistent chemistry will find they need a drain every two to three years rather than five to seven. This is not a sign of poor maintenance. It is the predictable result of filling and topping off a pool repeatedly with some of the hardest water in California.
When a Partial Drain Makes More Sense
A full drain and restart is the most thorough reset, but it is not always necessary. A partial drain, where you remove 25 to 50 percent of the pool water and replace it with fresh water, can be effective when:
Calcium hardness is elevated (400 to 600 ppm) but not severely so
TDS is climbing but chemistry is still manageable
You want to dilute accumulated stabilizer (CYA) without a full drain
Budget or timing makes a full drain impractical
A partial drain cuts the refill time roughly in half and costs proportionally less in water charges. For many Fresno pools, a partial drain every one to two years can extend the interval between full drains significantly.
Should You DIY or Hire a Professional?
Draining a pool without professional oversight carries real risks in Fresno, particularly around timing and hydrostatic pressure.
Hydrostatic pressure refers to the force that groundwater exerts against the outside of an empty pool shell. If the water table around your pool is high, or if unexpected rain saturates the soil while your pool is empty, this pressure can crack, shift, or in severe cases lift a concrete pool shell entirely out of the ground. A "popped" pool can cost tens of thousands of dollars to repair.
A professional pool service manages these risks through proper timing, correct use of hydrostatic pressure relief valves, and working efficiently to minimize the time the pool sits empty. In Fresno's climate, where summer heat adds the additional risk of surface damage to an empty shell, getting the drain and refill done efficiently and correctly the first time is worth the investment.
NTS Pool Services handles drain and restart services throughout Fresno, Clovis, Sanger, Reedley, Dinuba, and Madera Ranchos. We manage the full process from draining through chemical startup, and we communicate clearly at every step so you know exactly what to expect and when your pool will be ready.
The Bottom Line
A pool drain and refill is a two to four day process from start to swim-ready. The draining itself is relatively fast. The refilling is the time commitment, and the chemical startup is the phase that determines whether your pool is actually ready when you get back in.
In Fresno's hard water environment, a drain and restart is a predictable part of pool ownership, not a crisis. Understanding the timeline, the costs, and the risks lets you plan for it correctly and make sure it is done safely.
NTS Pool Services is a locally owned pool care company based in Fresno, CA. We provide weekly pool service, green pool cleanup, drain and restart, filter cleaning, pool repairs, and chemical balancing throughout Fresno and the Central Valley. Contact us for a quote.