Pool vs Open Water Swimming: Which Is Actually Better for Training?

If you’ve ever willingly got into freezing British water and called it “refreshing”… this blog is for you.

And if you’ve ever stared at a black line at the bottom of a pool questioning your entire existence… this one is for you too.

If you’re a swimmer or triathlete, you’ve probably wondered:

"Should I be doing most of my training in the pool, or should I be swimming in open water because that’s where I race?"

The answer is: both have a place — but they do different jobs.

For most triathletes, the pool should provide the majority of structured training, while open-water sessions should be used strategically to develop the skills and adaptability needed for racing.

As a practical starting point, something around 80–90% pool-based training and 10–20% open-water swimming can work well for many athletes.

As race day gets closer, the balance can shift towards more open-water work.

But there isn't a magic percentage that works for everyone.

So, let's look at why.

Pool Swimming: Where You Build the Engine

The pool gives you something that open water rarely can:

Control.

Distance, rest intervals, pace, stroke count and environmental conditions can all be standardised. That makes the pool particularly useful for developing fitness, refining technique and monitoring progression.

Benefits of Pool Swimming

1. You Can Develop Your Technique

In a pool, the environment is relatively predictable:

• Clear lane markings

• No waves

• No current

• Consistent distances

• Predictable turns

That means you can focus on things like:

• Body position

• Breathing

• Stroke mechanics

• Stroke rate

• Stroke length

• Pacing

• Coordination

It also makes it much easier to introduce a technical change and then repeat it over and over again.

Research comparing elite triathletes swimming in pool and open-water conditions has shown that swimmers actually change their mechanics between environments.

López-Belmonte et al. (2024) found that elite triathletes swam more slowly in open water while using a higher stroke rate and shorter stroke length, despite broadly similar physiological responses.

In simple terms:

The environment changes the way you swim.

That makes the pool a brilliant place to develop technical skills — but it doesn't mean those skills automatically transfer perfectly to open water.

The pool gives you the environment to develop the skill. Open water teaches you to apply it.

2. Your Training Is Easier to Measure

One of the biggest advantages of pool swimming is repeatability.

In the pool:

• 100 m is 100 m

• 400 m is 400 m

• Rest intervals can be controlled

• Pace can be monitored

• Stroke count can be recorded

• Stroke rate can be measured

• Sessions can be repeated and compared

For example, you might start with:

10 × 100 m @ 1:50

and, several weeks later, progress to:

10 × 100 m @ 1:48

while maintaining similar effort and technical quality.

That's useful information.

In open water, pace can be much harder to interpret because wind, current, drafting, water temperature and navigation can all influence performance.

And then there's the classic open-water experience:

“I'm sure I swam straight.”

Checks GPS.

Nope!

The more controlled the environment, the easier it is to measure change.

3. You Can Consistently Develop Fitness

Swimming performance isn't developed through one heroic session.

It comes from repeated exposure to appropriate training over time.

The pool makes it easier to consistently develop:

• Aerobic endurance

• Threshold performance

• Speed

• High-intensity capacity

• Technique

• Pacing

• Race-pace swimming

The environment is also much more predictable. No tides. No waves. No sudden changes in wind.

And, thankfully, no jellyfish plotting against you.

That consistency is incredibly useful when trying to progressively develop fitness.

Consistency is one of the pool's biggest strengths.

Limitations of Pool Swimming

The pool isn't perfect.

1. It Can be Predictable and Boring

Let's not pretend.

Swimming up and down a black line for an hour isn't always thrilling.

But boredom isn't necessarily a reason to abandon the pool. It might just mean your training needs a little more variety.

Good programming can include:

• Different interval structures

• Pacing challenges

• Technique work

• Pull and kick sets

• Race-pace swimming

• Skills-based sessions

• Partner sessions.........contact me it you need some inspiration in your sessions

2. It Doesn't Fully Replicate Open-Water Racing

This is probably the biggest limitation.

A pool can't completely reproduce:

• Mass starts

• Sighting

• Waves

• Currents

• Wind

• Variable visibility

• Physical contact

• Drafting

• Swimming around other athletes

• Navigation

• Buoy turns

And that's important because triathlon swimming isn't simply pool swimming without walls.

The environment changes the task.

Research in elite triathletes supports this distinction. Physiological responses can be broadly similar between pool and open water, while swimming mechanics and performance can differ.

Being fit enough to swim fast in the pool doesn't automatically mean you're ready to race well in open water.

3. Pool Turns Give You a Little Help

A 25 m pool contains a lot of turns.

Those turns allow you to:

• Push off the wall

• Streamline

• Change direction

• Briefly alter the demands placed on your muscles

Open-water racing doesn't offer any of that.

For this reason, continuous swimming and longer repetitions can be useful alongside traditional pool sets when preparing for an open-water race.

Open Water Swimming: Where You Learn to Apply It

Open water is where swimming becomes much less predictable.

And that's exactly why it deserves a place in your training.

Benefits of Open-Water Swimming

1. It Provides Race-Specific Practice

If you're racing a triathlon, you need to practise the skills required by triathlon swimming.

That includes:

• Sighting

• Swimming straight

• Navigation

• Drafting

• Turning around buoys

• Swimming close to other athletes

• Starting at race intensity

• Maintaining technique when fatigued

You simply can't reproduce all of these things by swimming lengths in a pool.

This is where specificity becomes important.

Training should expose you to the demands you're ultimately expected to perform.

You don't need every session to look like a race.

But some of them should.

The pool develops the foundations. Open water teaches you to use them.

2. It Develops Adaptability

Open water introduces variability.

The water might be:

• Calm

• Choppy

• Cold

• Warm

• Clear

• Murky

• Busy

• Quiet

Your job isn't to make the conditions perfect. Your job is to adapt to them while maintaining effective movement and decision-making.

This is one of the reasons open-water practice is so valuable for triathletes.

The aim isn't simply to become comfortable when conditions are perfect.

It's to become competent when they're not.

3. It Can Build Confidence

Confidence in open water shouldn't come from simply telling yourself:

“You'll be fine.”

It comes from experience.

The more opportunities you have to practise:

• Controlled breathing

• Sighting

• Swimming alongside other people

• Starting hard and settling

• Dealing with contact

• Navigating

• Responding to changing conditions

the more strategies you have available when something unexpected happens during a race.

And let's be honest, something unexpected usually happens.

Limitations of Open Water Swimming

1. Conditions Can Change the Training Stimulus

Open water is inherently variable.

Wind, waves, current and temperature can all affect the swimming experience and potentially influence performance.

That variability is useful for race preparation, but it can make open water less suitable for precisely controlling a training session.

If you planned a threshold session based on pace, for example, a strong current could make your pace data almost meaningless.

That doesn't make the session bad.

It means you need to interpret the session differently.

In open water, RPE, heart rate and technical quality can sometimes provide more useful information than pace alone.

2. Your Technique Won't Always Look the Same

As the environment changes, so can your stroke.

Remember the elite triathletes from the López-Belmonte study? Their open-water swimming involved a higher stroke rate and shorter stroke length compared with pool swimming.

That's important.

If your open-water stroke looks slightly different from your pool stroke, that isn't necessarily a technical failure.

The question is:

Is the adaptation helping you deal effectively with the environment while maintaining performance?

Open-water technique is about function, not simply trying to copy your pool stroke perfectly.

So Why Not Just Swim 100% Open Water?

If you race in open water, it seems logical:

“Shouldn't I do all my training in the environment where I race?”

Not necessarily.

Training is about developing different qualities, and different environments provide different opportunities.

Think about it like this:

🏊 Pool = Development

• Fitness

• Technique

• Pacing

• Repeatability

• Progressive overload

• Monitoring

🌊 Open Water = Application

• Sighting

• Navigation

• Drafting

• Race starts

• Environmental adaptation

• Decision-making

• Specificity

You need both.

The pool provides an excellent environment for developing the underlying physical and technical qualities required for swimming performance.

Open water then allows you to apply those qualities in the environment where you'll actually race.

So What's the Ideal Training Split?

There isn't strong evidence supporting one universal percentage split for every swimmer.

Your ideal balance will depend on:

• Your experience

• Your race distance

• Your technical ability

• Access to open water

• Confidence

• Time of year

• Competition calendar

• Individual weaknesses

However, as a practical coaching starting point, many triathletes can benefit from completing the majority of their structured swimming in the pool.

For example:

General Preparation

80–90% pool 10–20% open water

Focus on building fitness, technique and consistency.

As Competition Approaches

70–80% pool 20–30% open water

Increase the emphasis on race-specific skills and environmental exposure.

Race-Specific Period

Open-water sessions can become more frequent where appropriate, particularly when athletes need to practise:

• Race starts

• Sighting

• Drafting

• Buoy turns

• Continuous race-pace swimming

• Swimming in groups

• Adapting to conditions

The exact split should be determined by the athlete rather than following a rigid formula.

The Bottom Line

So, which is better?

Neither.

They're different environments with different strengths.

If your goal is to become a faster, more efficient swimmer, the pool provides an excellent environment for controlled, repeatable and progressive training.

If your goal is to perform well in an open-water triathlon, you also need to practise the technical, perceptual and environmental demands of open-water swimming.

The strongest approach isn't:

Pool OR open water.

It's:

Pool + Open Water

Build your fitness and technical foundation in the pool.

Then take those skills into open water and learn how to use them when the environment becomes unpredictable.

Because ultimately, the best swimmer isn't necessarily the person who can swim the fastest 400 m in a pool.

It's the person who can swim effectively when it actually matters.

Whether you're preparing for your first open-water triathlon or looking to improve your next race, the aim is the same:

Train with purpose. Develop the fundamentals. Practise the specifics. Race with confidence.