Every pool loses water. The question is whether the amount you are losing is normal, or whether something is wrong and getting worse.
Most guides frame this as a simple either/or: evaporation or leak. But after inspecting hundreds of pools across Charleston, Mount Pleasant, Summerville, and the surrounding Lowcountry, we have found that the real answer often falls into a third category that most homeowners and even some pool professionals overlook: surface-related water loss.
A pool surface that has become porous, cracked, or structurally compromised can lose water gradually, at a rate that does not look like a dramatic leak but consistently exceeds normal evaporation. This kind of water loss does not show up on a plumbing pressure test because the plumbing is fine. It does not get fixed by a new gasket or a pipe repair. It gets fixed by addressing the surface itself.
This guide walks through all three categories, how to distinguish them, and when each type of fix actually applies.
How Much Water Loss Is Normal?
In South Carolina’s humid climate, a pool without a cover typically loses about a quarter inch of water per day to evaporation during the warm months. On particularly hot, windy days, that number can approach a half inch.
Over a week, that adds up to roughly 1.5 to 2 inches of water loss from evaporation alone. Depending on pool size, that can be 300 to 500 gallons, which looks alarming if you are not expecting it.
A few factors that increase normal evaporation in the Lowcountry:
- Heated pools. Raising the water temperature widens the gap between water and air temp, especially overnight. This is the single biggest evaporation accelerator.
- Water features. Fountains, spillovers, and cascades increase surface area exposed to air and dramatically increase evaporation.
- Wind exposure. Pools in open, unsheltered locations lose more. Barrier island properties with consistent wind exposure lose noticeably more.
- No cover. A pool cover reduces evaporation by up to 95%. Most residential pools in South Carolina are uncovered.
If your pool is losing a quarter inch per day or less, and the rate stays roughly consistent with weather conditions, you are almost certainly looking at normal evaporation.
If you are losing more than that, consistently, something else is going on.
The Bucket Test: The First Thing to Do
Before calling anyone, run this test. It costs nothing, takes 24 hours, and tells you whether the water loss is normal.
- Fill a 5-gallon bucket about three-quarters full with pool water.
- Place the bucket on the first or second step of the pool, weighted so it does not tip. The bucket needs to sit in the same sun, wind, and air exposure as the pool.
- Mark the water level inside the bucket and the pool water level on the outside of the bucket with tape or a waterproof marker.
- Leave it for 24 hours. Do not use the pool during the test.
- Compare the two marks.
If both levels dropped the same amount: the water loss is evaporation. The bucket and the pool were exposed to the same conditions, and they lost water at the same rate. No leak.
If the pool level dropped noticeably more than the bucket: the pool is losing water to something other than evaporation. That “something” could be a plumbing leak, a fitting leak, or a surface problem.
Run the test twice. Once with the pump running on its normal schedule, once with the pump off for 24 hours. This second step narrows the location:
- If the pool loses more water with the pump running, the leak is likely on the pressure side of the plumbing: return lines, equipment connections, or underground pipes that are only pressurized when the pump is on.
- If the pool loses the same amount with the pump on or off, the leak is more likely in the pool shell itself: the surface, a crack, a failed fitting, or a structural issue.
That second result is the one most relevant to what we do.
The Three Categories of Pool Water Loss
Category 1: Plumbing and Equipment Leaks
These are leaks in the pipes, connections, fittings, and equipment that circulate the water. Common sources include corroded pipe joints, failing pump seals, loose or cracked fittings at the skimmer body or return inlets, and underground pipe damage from ground movement or root intrusion.
How to spot them: Wet ground near the equipment pad. Air bubbles coming through the return jets. Water loss that increases when the pump is running. Visible dripping at equipment connections.
Who fixes them: A plumbing or leak detection specialist. This is not resurfacing work, and we are straightforward about that. If your bucket test indicates a pressure-side plumbing leak, the right call is a qualified leak detection professional, not a resurfacing contractor.
Category 2: Evaporation
Normal water loss driven by heat, wind, and humidity differential. It is not a problem to solve. It is a condition to manage.
How to manage it: Use a cover when the pool is not in use. Reduce water feature run time during peak heat. Monitor with the bucket test if you are ever unsure whether the loss rate has changed.
Category 3: Surface-Related Water Loss
This is the category that gets missed, and it is the one we see most often in our work across Charleston and the Lowcountry.
A pool surface that has degraded to the point where it is porous, cracked, or delaminated allows water to migrate through the shell gradually. It is not a dramatic leak. It is slow, diffuse moisture loss through a surface that is no longer functioning as a sealed barrier.
On concrete and gunite pools, this shows up as:
- Hairline cracks (crazing) in the plaster that have developed over years of thermal cycling. Each crack is a pathway for water to reach the substrate and escape.
- Delaminated plaster that has separated from the gunite underneath, creating voids where water collects and slowly migrates outward.
- A surface that has become porous with age. Plaster is porous by nature, and it becomes more porous as it ages. In Charleston’s salt-air environment, this process is accelerated because salt-laden humidity drives mineral leaching from the cement matrix faster than in inland or dry climates. Eventually, the plaster is porous enough that it is effectively “weeping” water at a rate that exceeds evaporation but does not register as a discrete leak.
On fiberglass pools, surface-related water loss shows up as:
- Osmotic blistering. Moisture migrates through micro-cracks or imperfections in the gel coat and collects between the gel coat and the fiberglass laminate, forming blisters. The gel coat is no longer a sealed barrier.
- Gel coat cracking. Stress fractures in the gel coat, often around fittings, steps, or areas where the shell has flexed, create pathways for slow water loss.
- Gel coat deterioration. An oxidized, chalking gel coat that has lost its resin integrity is no longer non-porous. It allows moisture migration at a rate that is slow but persistent.
The reason this category gets missed is that the water loss is subtle. A pool losing an extra eighth or quarter inch per day from surface porosity looks like evaporation, and it does not show up on a plumbing pressure test because the plumbing is fine. Many homeowners spend months chasing a plumbing leak that does not exist, when the actual problem is the surface.
How We Diagnose Surface-Related Water Loss
When a homeowner contacts us after a leak detection specialist has cleared the plumbing and the pool is still losing water, the inspection shifts to the surface.
What we look for:
Texture changes. A surface that has become rough, chalky, or sandy to the touch has lost its original density and is almost certainly more porous than it was when it was installed. On plaster, this means the cement matrix has eroded. On fiberglass, it means the gel coat has oxidized past its functional life.
Visible cracks. We distinguish between surface cracks (in the plaster only) and structural cracks (through the gunite or fiberglass). Surface cracks are addressed during resurfacing. Structural cracks require repair before any new finish is applied.
Delamination. Tapping the surface with a coin or small tool reveals hollow spots where the finish has separated from the substrate. These areas are not just cosmetic. They are water pathways.
Blistering on fiberglass. Visible or palpable blisters on a fiberglass pool wall indicate moisture has already penetrated the gel coat. The number, size, and location of blisters tell us how far the problem has progressed.
Staining patterns. Certain staining patterns, particularly rust-colored staining radiating outward from cracks or fittings, can indicate that water is actively migrating through the shell and carrying dissolved minerals with it.
Water chemistry history. A pool that chronically loses chlorine faster than expected, or that requires significantly more chemical input than it used to, is often losing treated water through the surface and replacing it with untreated fill water. The chemistry instability and the water loss are symptoms of the same underlying surface failure.
When Resurfacing Fixes the Problem
If the water loss is coming through a deteriorated, porous, or cracked pool surface, resurfacing with a non-porous coating addresses the root cause directly.
aquaBRIGHT for concrete and gunite pools and polyFIBRO for fiberglass pools create a sealed, non-porous thermo-polymer membrane bonded to the pool shell. Water cannot migrate through the coating the way it does through aged plaster or failed gel coat. The surface stops being a pathway and starts functioning as the barrier it is supposed to be.
We handle structural surface repair as part of the process. Cracks are repaired, delaminated areas are addressed, and the substrate is prepared before the coating goes on.
When Resurfacing Does Not Fix the Problem
We are direct about this: resurfacing is not the answer for every pool that loses water.
If the water loss is coming from a plumbing leak, a failed underground pipe, or a corroded fitting on the equipment pad, no amount of surface coating will stop it. The plumbing needs to be repaired by someone who specializes in that work.
If the pool shell has significant structural movement, major displacement cracks, or settlement issues, resurfacing alone is not sufficient. The structural problem needs to be addressed first before any surface work makes sense.
We will tell you if resurfacing is the right fix. And if it is not, we will tell you that too. There is no value in coating a surface over a problem that lives somewhere else.
What Charleston’s Climate Does to This Timeline
South Carolina’s coastal environment accelerates surface-related water loss in ways that are worth understanding.
Salt-laden humidity from the Atlantic and the Intracoastal Waterway penetrates porous plaster and speeds up mineral leaching from the cement matrix. This makes plaster surfaces in Mount Pleasant, Daniel Island, and the barrier islands become porous faster than identical plaster in a drier, inland market.
Over 210 sunny days per year oxidize fiberglass gel coats on a compressed timeline, weakening the resin layer that keeps the gel coat sealed.
High water tables in areas like Johns Island, James Island, and parts of West Ashley create hydrostatic pressure against the pool shell, which can stress the surface from underneath and accelerate blistering on fiberglass and cracking on concrete.
These are not hypothetical risks. They are the conditions we see influencing pool surfaces across the Lowcountry every week.
Frequently Asked Questions
How do I know if my pool is leaking or just evaporating?
Run the bucket test. Place a bucket of pool water on a step, mark both water levels, and wait 24 hours. If the pool drops more than the bucket, you have water loss beyond evaporation. Run the test twice (pump on, pump off) to help narrow the source.
Can a deteriorating pool surface cause water loss?
Yes. Cracked plaster, delaminated surfaces, osmotic blistering on fiberglass, and surfaces that have become porous with age can all allow water to migrate through the pool shell gradually. This type of water loss often mimics evaporation and does not show up on a plumbing pressure test.
Should I call a leak detection company or a resurfacing company first?
If the bucket test shows water loss beyond evaporation, start with leak detection to rule out plumbing issues. If the plumbing checks out and the pool is still losing water, the surface is the next thing to evaluate. That is where we come in.
How much water loss is normal for a pool in South Carolina?
About a quarter inch per day during the warm months, potentially more on hot, windy days or if the pool is heated or has water features. Consistent loss beyond that rate, especially in mild weather, is worth investigating.
Not Sure What You Are Dealing With?
If your pool is losing water and you are not sure whether the surface is part of the problem, we offer free on-site inspections across Charleston, Mount Pleasant, Summerville, Daniel Island, Goose Creek, and the surrounding Lowcountry. We will evaluate the surface, tell you honestly what we find, and recommend next steps, even if those next steps are not resurfacing.
Call 854-444-9416 or schedule your free assessment here.