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How Much Should You Fill A Hot Water Bottle?

Updated: Jan 21, 2023

Hot water water filling recommendation

Your hot water bottle should be filled with no more than two-thirds of its total capacity. By filling it up to full capacity, too much pressure is applied from the inside. This can lead to your bottle bursting and cause serious burn injuries. For the same reasons, gently push the air out of your hot water bottle when filling it.

Why you should fill your hot water bottle up to two-thirds

The main reason you want to stick by the two-thirds rule is safety. Filling your hot water too much may lead the material to gradually stretch and degrade itself or burst altogether. Your hot bottle bursting during use can cause severe burn injuries.

In addition, this "hot water bottle two-thirds rule" comes from the official British Standards (BS1970:2012) instructions for consumers. The British Standards Institution (the national standards body of the United Kingdom) also determines the quality standards for hot water bottle manufacturers.

Picture of hot water bottle British Standards

How to fill a hot water bottle safe for use: 4 steps

Here are a few basic steps you can follow to make sure you don't overfill your hot water bottle.

If you are not used to filling a hot water bottle, we advise you to try this with cold water to prevent burns and injuries.

Steps to safely fill a hot water bottle

1. Check for leaks

Check your hot water bottle is in good shape and has no tears or visible damage. Perform a test by pouring a bit of cold water into it, screwing the stopper on, and squeezing it over the sink to check for leaks.

Once your test is completed and successful, pour that water into your kettle (let's save water!). If your hot water bottle is leaking, do not use it. Dispose of it and purchase a new one.

2. Fill it up by two-thirds

Fill your hot water bottle aiming for not more than two-thirds of its total capacity. If you're not exactly sure how to calculate the amount you're pouring, take your time and do it gradually by gently squeezing the bottle to get an idea of the water level.

3. Squeeze the air out

Once your hot water bottle is filled, make sure to gently squeeze the air out before sealing it with the stopper. Trapping air inside your hot water bottle may cause too much pressure on the inside and increase the chances of your hot water bottle bursting during use.

4. Screw the stopper on

Once you've squeezed the air out, screw the stopper on. Carefully turn the hot water bottle upside down over your sink to check it is correctly sealed. If there are no drips or small leaks, you're good to go! If you even have a slight suspicion of minor leaks, screw the stopper off and back on again.

If you're still seeing leaks after a new test, your hot water bottle is damaged and no longer usable with hot water. Purchase a new one to prevent accidents.

After you fill your hot water bottle and screw the stopper on, use a cloth to dry the mouth of your bottle to make sure you don't burn yourself with water residue.

Final thoughts

Using a hot water bottle can be beneficial in many ways. Most individuals used them to keep warm, especially in times when we seek ways to save energy. Regardless of how you use it, it's important to remain safe at all times and follow instructions of use given by manufacturers to prevent accidents.

Hot water bottles can be your greatest friends during winter, as long as you make sure to take care of them and use them wisely!


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