electrically heated hot water will cost you a fortune.... about 4 times the cost if it was gas....
£70 a month doesnt sound that far out....
my parents once had a £3000 electric bill.... every time the meter was read they assumed it had been read wrong and sent an estimated bill instead... few years later and my father checked the meter himself and was more than a little shocked... (tho i was very tempted to turn it back!)