Ok, I shall not profess that the following is a definitive answer to your question, but it is an educated speculation. This word corresponds very much with a classical Arabic lexeme, both in its meaning and pronunciation as it is evident by your reference to ‘shower’ (And I mean according to the British accent, which I assume you speak, and hear howwa uttered in). The Arabic lexeme, still used today as well, is howa (هو). While it means ‘he,’ it can also mean ‘this thing’ or ‘that thing,’ because Arabic is a gender-based language. This means that, in Arabic be it used classically or colloquially, you can refer to a ‘thing’ as ‘he’ if it is recognized by Arabic native speakers as ‘male.’
While this sounds a little off, there is ample etymological evidence that some European words could be traced to Arabic due to the cultural permeation in Medieval times, enabled by then Moslem Spain. Prime examples of loan words are ‘rice,’ ‘potato,’ ‘cotton,’ and ‘tomato,’ yet the source language is often a matter of uncertainty. One word surely adopted from Arabic is ‘Saracen,’ meaning a ‘Moslem,’ during the time of Crusades, as it was used by poets such as Jeffery Chaucer. It fact, this word represents an ethnicity, and not a religion; yet, since the Moslem leader Saladin was a Circassian (شركسي), there is a very high probability the word ‘Saracen’ accordingly was adopted to refer to Moslems in general.
To answer your question directly: I think, based on similar cases, the word in question could be traced to Arabic roots. If you are interested in this subject, I highly recommend reading:
1) The Matter of Araby in Medieval England. By Dorothee Metlitzki
2) The Arabic Role in Medieval Literary History: A Forgotten Heritage. By Maria Rosa Menocal.
I hope this participation can at least open possibilities of further research for you.