How Long Does a Pool Drain and Refill Take? (Honest Timelines for Fresno Homeowners)
By Nancy Padjan | 9 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 project of one to two weeks from initial permit application to swim-ready, with the drain and refill itself taking two to four days once the permit is in hand.
That timeline breaks down into distinct phases: applying for the city permit, 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 and regulatory environment, the risks of getting any of this wrong are higher than in more temperate parts of California.
Here's a clear, realistic breakdown of the entire process.
Phase 0: The Fresno Permit Question
Before any pump goes in the water, there is a step most Fresno pool owners do not realize exists.
Every pool drain and refill in Fresno requires a Short-Term Exemption Application filed with the City of Fresno Water Division at least 48 hours in advance. This is true whether it has been five years since your last drain or six months. The reason is that a normal residential refill takes 30 to 50 hours of continuous water flow, and Fresno's Outdoor Water Use Schedule only allows outdoor water use on alternating days based on your address. A refill cannot fit inside a single allowed watering day, so the exemption permit is what authorizes you to run water outside the normal schedule for the duration of the project.
If it has been more than three years since your last drain: the application is essentially a scheduling step. You submit at least 48 hours in advance, the city reviews and approves, and you proceed with the drain and refill on the approved dates.
If it has been less than three years since your last drain: the application requires additional supporting documentation justifying the early drain. Per Fresno Municipal Code Section 6-520(a)(16), customers are not permitted to drain swimming pools more than once every three years, except as necessary to complete structural repairs or to comply with public health standards. The code recognizes specific water chemistry conditions as qualifying reasons. The most common ones are cyanuric acid above 100 ppm, elevated total dissolved solids, or calcium hardness that has climbed beyond chemical management. Your supporting documentation has to include an independent water test (not a strip from the pool store) showing the qualifying numbers. You can read more about the CYA side of this in our post on why we sometimes skip the chlorine tabs in your floater.
The rule applies to the water customer at the property, not the pool service company. Whether you drain the pool yourself or have us do it, the homeowner is the one responsible for compliance and the one whose account would be cited for a violation.
The permit application adds two to five business days to the front end of any drain project, regardless of which scenario you fall under. Plan accordingly.
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 for 24 to 48 hours, 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 Fresno Metropolitan Flood Control District also notes that residents may need a separate permit to discharge to the street, and that chlorine must dissipate for 24 to 48 hours after last treatment before the water can be released. The conservative path is sewer cleanout, every time.
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.
Why the refill needs the city permit
Because a 30 to 50 hour refill cannot fit inside a single allowed watering day, this is what the Short-Term Exemption Permit from Phase 0 actually authorizes: continuous outdoor water use for the duration of the project rather than only on your assigned alternating days. The standard schedule is:
Addresses ending in odd numbers: Tuesday, Thursday, Saturday
Addresses ending in even numbers: Wednesday, Friday, Sunday
That is why the permit step is universal, not optional. Without it, you are technically only allowed to refill on every other day, which both extends the project timeline significantly and risks violations recorded against your water account.
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 is worth taking seriously given Fresno's water conservation rules. 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 or CYA 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
A note on stabilizer at startup: this is the moment to set CYA correctly and not let it climb past where it needs to be. The right target is 30 to 50 ppm for a chlorine pool, or 60 to 80 ppm for a saltwater pool. Adding granular CYA directly gives precise control and avoids the tablet-driven creep that leads many pools right back into a high-CYA problem within a year or two of refill. If you just paid for a drain to fix high CYA, the last thing you want to do is start the new water on a tablet-only chlorine regimen. See our post on chlorine tabs and CYA for more on this.
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
Cyanuric acid is between 30 and 50 ppm (60 to 80 ppm for saltwater)
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 |
|---|---|
| City permit application | 2 to 5 business days |
| 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 | 1 to 2 weeks |
For a standard drain and restart without acid wash, the drain-through-startup work is two to three days of actual project time. With an acid wash, plan for three to four days of project time. The full one to two week range accounts for the permit application on the front end. These timelines assume work begins early in the morning on day one and that refilling runs continuously once the project is underway.
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 — and the three-year city rule is calibrated around that reality, allowing one drain per pool inside that window without requiring additional supporting documentation.
The reason comes back to two things: hard water, and stabilizer accumulation from chlorine tablets.
On the hard water side, 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.
On the stabilizer side, trichlor chlorine tablets add cyanuric acid to the water every time they dissolve. Over a Fresno summer with tabs running continuously to keep up with UV demand, CYA can climb 50 to 100 ppm in a single season. Once CYA passes 100 ppm, the pool stops responding to chlorine the way it should, and dilution becomes necessary. The way to prevent that is switching off tabs when CYA gets high and using liquid chlorine instead. Again, see our post on the topic.
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, and of relying on tablets as the only chlorine source.
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.
A partial drain still counts as a drain under the three-year rule, so the same permit considerations apply if you are inside that window.
Should You DIY or Hire a Professional?
Draining a pool without professional oversight carries real risks in Fresno, particularly around timing, surface damage, and avoiding the kind of mistakes that lead to hydrostatic problems.
A quick note on hydrostatic pressure, because it gets oversold in a lot of pool industry writing. Fresno sits over the Kings Subbasin aquifer system, where decades of groundwater pumping have left the water table tens to hundreds of feet below the ground surface throughout the city, which is well below the bottom of any backyard pool. The classic high-water-table popped-pool scenario, common in places like coastal Florida or parts of the Gulf Coast, is genuinely rare here. What does still happen occasionally is localized hydrostatic damage from soil saturation around the pool shell, which is almost always traceable to draining right before or during a winter storm, an unaddressed irrigation leak near the pool, drain discharge being routed back toward the pool instead of away, or an old hydrostatic relief valve that has failed silently. None of these are about the regional water table. They are about avoidable mistakes in how and when the drain is done.
A professional pool service manages these risks through proper timing (no winter-storm drains, no leaving the pool empty overnight in summer), correct use of hydrostatic pressure relief valves, routing discharge well away from the structure, and working efficiently to minimize the time the pool sits empty.
NTS Pool Services handles drain and restart services throughout Fresno, Clovis, Sanger, Reedley, Dinuba, and Madera Ranchos. We manage the full process from permit application 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 in Fresno is a one to two week project from initial permit application to swim-ready, with the drain and refill itself taking two to four days once the permit is in hand. The draining itself is relatively fast. The refilling is the time commitment, the city schedule shapes when that refill can happen, 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, the city's rules, and the chemistry choices you make right after the refill lets you plan for it correctly and make sure it is done safely, and lets you stretch the interval between drains as long as possible.
This post is for general informational purposes and reflects Fresno water rules and pool industry practices as of the publication date. Municipal codes, water conservation stages, and city schedules can change. Always verify current rules with the City of Fresno Water Division before applying for a permit or scheduling a drain. Every pool is different, and the right approach for your specific pool depends on its construction, condition, age, and water chemistry. Nothing in this post is a substitute for an on-site assessment by a licensed pool professional.
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.