How to Clean a Soft Flask and Keep Your Water Tasting Fresh

There’s nothing worse than reaching for your soft flask halfway through a run and getting a mouthful of an unpleasant plastic, stale or musty taste.

Whether you're using a soft flask for running, hiking, cycling, the gym or everyday hydration, keeping it clean and properly dried is the best way to prevent unwanted tastes and smells.

The good news is that cleaning a soft flask doesn't need to be complicated. In most cases, rinsing it after every use, allowing it to dry completely and storing it open will keep it fresh.

If your soft flask already has a taste or smell, there are a few additional methods you can try, including bicarbonate of soda (baking soda), lemon juice and the freezer method.

Here's everything you need to know about keeping your soft flask tasting fresh.

Why does my soft flask taste bad?

A soft flask can develop an unpleasant taste or smell for several reasons.

The most common causes are:

• Leaving water or sports drink inside the flask for too long
• Storing the flask while it is still damp
• Residue from electrolyte or carbohydrate drinks
• A new flask having a slight plastic taste
• Not cleaning the cap or mouthpiece properly
• Storing the flask sealed rather than allowing air to circulate

The good news is that most of these problems are easy to prevent.

The most important habit is simple: rinse your soft flask after every use and allow it to dry completely before storing it.

How to clean a soft flask

For everyday cleaning, you don't need anything complicated.

After every use:

1. Empty the flask

Don't leave water, electrolyte drinks or energy drinks sitting inside the flask after your run.

2. Rinse thoroughly

Fill the flask with clean water, shake it and empty it. Pay particular attention to the opening, cap and mouthpiece.

3. Wash when necessary

For a deeper clean, use warm water and a small amount of mild washing-up liquid.

4. Rinse thoroughly

Make sure you remove any remaining soap before using the flask again.

5. Leave it open to dry

This is one of the most important steps. Leave the flask and cap open so that air can circulate inside.

6. Store it completely dry

Once dry, store your soft flask somewhere clean and dry until you're ready to use it again.

How to get rid of a plastic taste in a new soft flask

A slight plastic taste can sometimes be noticeable when using a new soft flask for the first few times.

This doesn't necessarily mean there is anything wrong with the flask. Some people are simply more sensitive to the taste or smell of new plastic than others.

Start with a thorough rinse using clean water.

If you can still taste it, try the lemon and freezer method.

The lemon and freezer method

HydraPak, a specialist hydration equipment manufacturer, recommends using lemon juice and freezing a soft flask to help reduce unwanted taste. 

Here's how:

1. Fill your soft flask with water.
2. Add approximately one teaspoon of lemon juice.
3. Leave some space at the top of the flask — don't fill it completely.
4. Place the flask in the freezer overnight.
5. Allow it to thaw completely.
6. Empty and rinse thoroughly with fresh water.
7. Leave it open to air dry.

Why leave space in the flask?

Water expands when it freezes, so don't completely fill a sealed flask before putting it in the freezer.

This method can be particularly useful if you're trying to remove a plastic taste from a new soft flask.

How to clean a soft flask with bicarbonate of soda

If your soft flask has developed a persistent smell or taste, bicarbonate of soda (also called baking soda) is another simple option. Trekkrs' Elite Soft Flasks come with two sachets to help get you off to the best start.

How to use bicarbonate of soda:

1. Fill the flask with warm water.
2. Add a small amount of bicarbonate of soda.
3. Allow it to soak for around 30–60 minutes.
4. Empty the flask.
5. Rinse thoroughly with clean water.
6. Leave the flask open to dry completely.

Bicarbonate of soda can be particularly useful when you're dealing with stale smells or lingering flavours from sports drinks.

If you're sensitive to taste, give the flask an additional rinse with fresh water before using it.

How to remove an electrolyte drink taste from a soft flask

If you use your soft flask for electrolyte drinks, energy drinks or carbohydrate mixes, you may notice that the flavour can linger even after you've emptied it.

This is because drinks containing sugars, flavourings and other ingredients can leave residue inside the flask.

The best way to prevent this is to rinse your flask immediately after use.

If a flavour has already developed:

• Wash it with warm water and mild washing-up liquid.
• Rinse thoroughly.
• Try a bicarbonate of soda soak if the flavour remains.
• Allow it to dry completely before storing.

For particularly persistent tastes, the lemon/freezer method is another option.

How to get rid of a bad smell from a soft flask

A musty or stale smell is often a sign that moisture has been trapped inside the flask.

This is particularly easy to do with soft flasks because their flexible construction can make it tempting to rinse them and immediately put them away.

Instead, always dry your soft flask with the opening fully exposed to air.

For an existing smell:

1. Wash the flask thoroughly.
2. Clean the cap and mouthpiece.
3. Rinse several times.
4. Use a bicarbonate of soda soak if necessary.
5. Leave the flask open until completely dry.

Don't simply screw the cap back on while the inside is still damp.

Don't forget the soft flask cap and mouthpiece

When cleaning a soft flask, it's easy to concentrate on the bottle itself and forget about the cap.

However, small amounts of liquid can remain around the drinking opening or mouthpiece.

If your water tastes fine from another bottle but tastes strange when drinking from your soft flask, the cap or mouthpiece is worth checking.

Give removable components a thorough rinse and clean them according to the manufacturer's care instructions.

Should you put a soft flask in the freezer?

Yes, freezing can be used as part of a cleaning method for some soft flasks, but you should always follow the care instructions for your particular product.

If you're using the lemon/freezer method, leave room for the water to expand as it freezes and allow the flask to thaw completely before rinsing.

Freezing should be considered an occasional method for tackling taste rather than a replacement for normal cleaning and drying.

Should I use lemon juice, vinegar or bicarbonate of soda?

There are lots of different soft flask cleaning methods suggested online.

You don't need to use all of them.

For normal cleaning, warm water, mild washing-up liquid and thorough drying should be your starting point.

For persistent tastes or smells, bicarbonate of soda can be useful.

For a new flask with a noticeable plastic taste, the lemon and freezer method is another option.

If you use any cleaning product, rinse the flask thoroughly afterwards.

Most importantly, don't mix different cleaning chemicals together.

How to keep your soft flask tasting fresh

Prevention is much easier than trying to remove a bad taste later.

Follow these five simple habits:

1. Rinse after every use

Especially after using electrolyte or carbohydrate drinks.

2. Don't leave drinks sitting inside

Empty your flask as soon as possible after finishing your run.

3. Clean the mouthpiece

Don't forget the cap and drinking opening.

4. Dry it completely

Leave the flask open so air can circulate inside.

5. Store it open and dry

Avoid sealing a damp flask away in your running kit.

These simple steps will dramatically reduce the likelihood of developing unpleasant tastes and smells.

Quick guide: common soft flask problems and solutions

Problem	What to try
New flask tastes of plastic	Thorough rinse, then try the lemon + freezer method
Stale or musty smell	Wash thoroughly, use bicarbonate of soda and dry completely
Tastes like an electrolyte drink	Rinse immediately after use and deep clean if necessary
Water tastes strange	Clean the flask, cap and mouthpiece
Flask smells after storage	Make sure it is completely dry before storing
Taste keeps returning	Review how quickly you're rinsing and whether the flask is being stored damp

The Trekkrs 60-second soft flask routine

If you don't want to remember a complicated cleaning routine, just remember:

Empty → Rinse → Dry → Store

Empty your flask after every run.

Rinse it thoroughly with clean water.

Dry it completely with the opening left open.

Store it somewhere clean and dry.

That's it.

If you've already developed a persistent taste or smell, try a deeper clean with bicarbonate of soda or, for a new flask with a plastic taste, the lemon and freezer method.

Fresh flask. Fresh water. Better runs.

Your hydration should be one less thing to worry about when you're running.

With a few simple habits, your Trekkrs soft flask can stay clean, fresh and ready for your next adventure.

Whether you're heading out for a quick 5K, a long training run, a hike or an ultra, look after your flask and your water will taste better for longer.

Empty. Rinse. Dry. Repeat.