If you want to wash your plastic drinking bottle, rinse it out and then turn it upside down so that the water can run off. Ideally, you should even dry it out. Stainless steel bottles are a good alternative - they are less likely to harbour bacteria. In addition, stainless steel bottles do not contain any of the controversial plasticisers.
According to many experts, it becomes dangerous when the substance bisphenol A (BPA) comes into play. It is a so-called plasticiser and was previously used in the production of many drinking bottles. If BPA enters the human body, its effects are similar to the female sex hormone oestrogen and can lead to infertility in men. Such or similar effects have been proven in animal experiments. BPA can be found in cheap drinking bottles from Asia. This is not always recognisable on the bottles. Many manufacturers advertise as "BPA-free". For orientation: If there is a triangle (plastic code) with an O in the centre on the bottle, the bottle could be made of the dangerous polycarbonate. Codes 1, 3 and 6 do not contain BPA, but may contain other hormone-like plasticisers.
Bacteria like it moist and prefer to settle on rough surfaces. Cracks or scratches are therefore particularly susceptible. Bacteria multiply even faster on the mouthpiece due to contact with saliva. If you fill your bottle with a sugary drink, you are fuelling bacterial production many times over - because then the bacteria really have something to eat.
How long can you keep water in a plastic drinking bottle without it becoming unsafe? The question is not so easy to answer. "Ideally, you should change the water every day," says microbiologist Dr Claudia Beimfohr. The decisive factor is what kind of bacteria get into the bottle and how strong the drinker's immune system is. Some people have no symptoms if the water has been standing for a week or longer - others do. In the worst case, there is a risk of diarrhoea and nausea. If this doesn't happen to you, you don't need to worry any more - you are strengthening your immune system.
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