The opening is just big enough for me to reach all of the interior of the jar with a sponge for cleaning. I had just purchased a device for structuring water (a wand that you stir with made of "mother water" inside quartz crystal) and wanted a special vessel to hold our coherent water in. The combination is great, feeling healthier and happier since starting this ritual. If you are attracted to a product like this you probably are also open to the idea of water being more than just H2O molecules, and would benefit from honoring and respecting it with this kind of container!