Distilled water is water that has had many of its impurities removed through destillation.
Distillation involves boiling the water and then condensing the steam into a clean container. After opening the container it’s possible for bacterial spores to come in. Pseudomonas aeruginosa are capable of growing even in distilled water. Also the bacteria B.cepacia has been isolated from the screwed bottle neck of the container of distilled water five weeks after being opened.
Therefore do not use opened container of distilled water for longer than a week.
Instead, you can use rinsed tap water for the sterilization of your devices, if your tap water has drinking water quality. You can also use boiled tap water for at least 8 hours and save a lot of money.
Source: Medical University Children’s Clinic CF-Center at the AKH-Vienna