In last week's line graph essay I repeated the word "expenditure" four times. Is this a problem?
The answer is no! If you look at the graph, you can see that the whole essay must be about expenditure. In fact, I needed to mention the idea of expenditure eleven times! Does the examiner really expect you to think of eleven synonyms for "expenditure"? Of course not.
It's impossible to avoid repeating some of the key words in writing task 1. Try to add variety where you can (I also used "spending", "spent" and "paid out"), but don't become obsessed with this. The important thing is to describe and compare the data.