Aquatic therapy billing is one of those things that seems straightforward until the first denial lands in your inbox.
I spent years running aquatic programs before I ever had to think about the coding side of it. The water doesn't care about CPT manuals, but the insurance companies do, and they will fight you on pretty much every claim you send their way if they can find a reason to. The code itself is simple. It is 97113 — aquatic (water) therapy. That is the only CPT code you need for direct, one-on-one therapeutic exercise in a pool. But the real work happens in everything around that code: documentation, medical necessity, payer-specific rules, and knowing when to pair it with something else and when to leave it alone. The code was created to capture structured therapeutic exercise performed in water. It is not a general swim lesson. It is not hydrotherapy in the spa sense where the patient is just soaking. It has to be active, goal-directed, and tied to a measurable rehabilitation objective. If your chart note reads "patient enjoyed swimming for 30 minutes" you are going to lose that claim. Every time. I learned that the hard way in 2016 when a carrier denied a month's worth of aquatic therapy because we had not documented the specific neuromuscular re-education objective we were targeting in the water. The carrier's utilization review nurse literally wrote that we had failed to differentiate the service from recreational swimming. It took us three months to get paid.
Cpt Code Aquatic Therapy
Here is how the code actually works in practice. You spend the session doing resisted movements, balance training, gait re-education, range-of-motion work, or strengthening — all while the patient is in a therapeutic pool at a temperature and depth that supports the treatment. The key differentiator is that the water provides resistance and buoyancy to modify the exercise load in ways that cannot be replicated on land at that stage of recovery. You do not need to spend the entire session in the water. If a meaningful portion of the treatment time is dedicated to aquatic-based therapeutic exercise, the code applies. Most carriers expect at least half the session, but the exact threshold varies by payer. The unit structure is time-based. You bill in 15-minute increments. If the patient spends 38 minutes in the water doing therapeutic exercise, that is two units. If they spend 12 minutes, that is one unit, because the minimum for any billed time is still one 15-minute block. This is different from some other therapy codes where you can bill based on a mix of techniques with different time structures. With 97113 it is purely water time spent on active treatment. What most people miss is the modifier situation. You will often pair 97113 with 97110 (therapeutic exercises) or 97530 (therapeutic activities) when you transition from the pool to dry land work in the same session. If you do 30 minutes of aquatic work and then 20 minutes of land-based strengthening, you are billing two units of 97113 and one unit of 97110. Some payers will stack these without issue. Others will flag it as unbundling if the documentation does not clearly separate the two environments and justify why both were medically necessary on the same day. I have seen claims denied for unbundling simply because the therapist wrote "treated lower extremity strength and balance" without explaining that the aquatic portion targeted proprioception through unstable water surface while the land portion focused on progressive resistance training. The procedures were different. The rationale needed to match on paper.
There is a second common mistake around the temperature requirement. If the pool water is heated for therapeutic reasons — which is almost always the case for older adults, patients with arthritis, or post-surgical populations — you should document the water temperature. Not for the code itself, but for the medical necessity argument. A carrier that questions whether aquatic therapy was appropriate will look at the temperature record and see that you maintained the pool at 88 to 92 degrees Fahrenheit specifically to reduce joint stress while allowing movement. That is a defensible clinical decision. Leaving it undocumented makes it look like you just used the pool because it was available. I ran into a particularly annoying edge case with Medicare in 2019 that I still think about. We were treating a patient with a recent total knee replacement who met the criteria for aquatic therapy, and the local coverage determination allowed it under certain post-surgical conditions. The problem was that the patient's primary diagnosis at the time was a fracture secondary to osteoporosis, not the arthroplasty itself. The carrier denied the claim because the fracture diagnosis did not clearly support aquatic therapy under their interpretation of the LCD. We had the surgical history in the chart. We had the physician's order specifying post-operative rehabilitation. But the claim was submitted with the fracture code as the primary, and the review stopped there. The workaround was straightforward once we figured it out: we switched the primary diagnosis to the complication code for the aftercare of the orthopedic surgery and added the osteoporosis code as secondary. The claim went through on the second submission. The lesson was that Medicare's LCD pathways for aquatic therapy are tied to very specific diagnosis clusters, and being clinically accurate on paper sometimes matters more than being accurate in the referral. I started cross-referencing each patient's diagnosis set against the payer's published LCD before scheduling aquatic sessions. It saved us from a lot of back-and-forth. Documentation is where the majority of denials originate. A complete note for 97113 should include the water temperature, the depth of the pool, the specific exercises performed, the patient's response to the buoyancy-assisted movement, the functional gains observed, and the progress toward the treatment plan goals. Do not write "improved range of motion." Write "achieved 110 degrees knee flexion in water versus 85 degrees on land, allowing progression to partial weight-bearing gait training." The numbers make the medical necessity defensible. They also make your audit trail clean if anyone ever asks why aquatic therapy was continued week after week.
Get the Full Details
There is a bottleneck that nobody talks about: the facility itself. Not every clinic has a therapeutic pool. Many therapists bill 97113 at centers that subcontract out to aquatics facilities, and the billing structure gets complicated fast. If you are the originating site and another facility is the furnishing site, you may need to use modifier GC or the appropriate place-of-service codes depending on the payer. Some commercial carriers have their own rules about split-site billing that differ from Medicare's. I once billed a claim with the wrong POS code for an aquatic therapy session at an external wellness center, and the denial cycle took six weeks because the carrier required a specific attestation from the furnishing site confirming that the equipment and personnel met their medical standards. Getting that attestation required a phone call to a different department at the facility, a fax that got lost, and a follow-up visit from the physical director. It was a waste of time that could have been avoided by understanding the payer's split-site requirements before the first session. Children's cases add another layer. Pediatric aquatic therapy is common for developmental delays, cerebral palsy, and sensory processing disorders. The code is the same — 97113 — but the documentation expectations shift. You need to show how the water environment facilitated motor planning, improved trunk control, or allowed weight-bearing activity that was impossible on a firm surface. I worked with a case involving a seven-year-old with spastic diplegia where the carrier initially denied the claim because the note did not clearly link the aquatic work to functional outcomes. We resubmitted with video documentation showing the child progressing from supported pool walking to independent step-over-obstacle tasks in chest-deep water. The carrier approved it on review. Video evidence is not required by most payers, but it is extremely useful when the functional gains are subtle and the clinical rationale needs visual reinforcement. The cost side of things is worth noting because it affects both the provider and the patient. Running a therapeutic pool is expensive. Heating, filtration, chemical balancing, lifeguard staffing, and accessibility modifications like pool lifts can run into tens of thousands of dollars annually. This means that many clinics simply do not offer aquatic therapy in-house anymore, which pushes patients toward specialized centers and increases travel time. Insurance coverage helps, but not all plans cover 97113 at the same rate. Some Medicaid programs do not cover it at all. Private insurers vary widely. A therapist considering starting or expanding an aquatic program should check the reimbursement rates for 97113 in their specific market before investing in facility upgrades. I have seen two clinics in the same city shut down their pools within a year of each other because the payer mix did not support the overhead.
For the therapist who is actually running the sessions, the clinical value is clear. Aquatic therapy allows early mobilization for patients who cannot tolerate full weight-bearing, provides a safe environment for balance training with reduced fall risk, and enables cardiovascular conditioning for patients who cannot perform land-based aerobic work. The resistance of water at different depths allows graded strengthening without heavy external loads. The hydrostatic pressure can reduce edema. The warmth improves tissue extensibility. These are not theoretical benefits. They are the reasons the code exists. The downsides are equally real. Patient throughput is low. You can only treat as many people as the pool lane count and depth allow, and safety ratios in the water are stricter than on land. Infection control is harder to manage. Scheduling is less flexible because pool availability is often the constraint, not therapist availability. Documentation burden is higher than for land-based sessions because carriers expect more detail to justify the added cost and complexity. And the reimbursement does not always reflect the actual resource intensity of running a pool-based service. Some payers reimburse 97113 at rates that barely cover the marginal cost of heating and chemically treating the water for a single patient session. If you are entering this space now, the practical steps are straightforward. Get the CPT manual or access the AMA's online coding database. Verify your payer's coverage policy for 97113 before enrolling a patient. Document the water temperature and depth in every note. Pair the code with the correct diagnosis and support it with functional outcome data. Use modifiers appropriately when combining modalities. Keep the attestation and facility paperwork current if you are using an external pool. And before you invest heavily in infrastructure, confirm that the reimbursement trajectory in your region supports the overhead.
The code is simple. The ecosystem around it is not. Anyone who tells you otherwise has not dealt with a denial review. The work is in the details, and the details are what separate a sustainable aquatic therapy program from a well-intentioned one that runs out of funding within a year.
