The present invention concerns a method for purification of contaminated water through hydrate formation and separation of hydrates from contaminated water enriched with contaminants, by supplying hydrate particles to the water during hydrate formation. The present invention also concerns a device for purification of water by using a method according to the invention, and water produced according to the invention. By using the process principles according to the present invention, all types of water can be purified for consumption or safe discharge, or desired resources can be recovered, and air can be purified if it first is bubbled through the water which then is purified by a method according to the invention.