One missing word can change the meaning.

OK it's petty, but I get bothered when I see the English language used poorly.  This sign amuses me everytime I see it.  The sign below is located on a fountain outside of the Art Gallery Of South Australia:

RECLAIMED WATER USED TO FILL THIS FOUNTAIN

Do they mean reclaimed water is used to fill the fountain?  Because whenever I read it, my mind reads it as reclaimed water used to fill the fountain but it doesn't anymore.  One little word (IS) can change the whole meaning.