Deionisation is a method for purifying water. Purified water is water taken from any source and then processed using various methods to remove impurities. Deionization and distillation are two such methods to purify water, but other processes can also be employed. Deionised water or demineralized water, is water that has had its mineral ions removed. It is a physical process using specially made resins to filter out the mineral salts from the water. The vast majority of impurities are dissolved salts and deionisation produces a high purity water that is similar to distilled water, without scale build up. Deionization however does not remove viruses or bacteria except by incidental trapping in the resins. Deionisation does not remove hydronium or hydroxide ions from the water as this would result in the removal of the water itself.