H serves many purposes.
One word, two or hyphenated?Edit
Sometimes a phrase becomes so common that it eventually becomes a single, commonly accepted word. Usually it begins as two words used together frequently, for example, dish washer. Often the two words are then joined with a hyphen, like water-bed. Over time the words may eventually join to become a compound word such as dish-washer becoming dishwasher. Sometimes words go the other way too, and what was a compound or hyphenated word becomes separate.