In trading on Tuesday, shares of the First Trust ISE Water Index Fund ETF ( FIW) entered into oversold territory, changing hands as low as $31.885 per share. We define oversold territory using the Relative Strength Index, or RSI, which is a technical analysis indicator used to measure momentum on a scale of zero to 100. A stock is considered to be oversold if the RSI reading falls below 30.In the case of First Trust ISE Water Index Fund, the RSI reading has hit 29.8 — by comparison, the RSI reading for the S&P 500 is currently 48.5. A bullish investor could look at FIW's 29.8 reading as a sign that the recent heavy selling is in the process of exhausting itself, and begin to look for entry point opportunities on the buy side. Looking at a chart of one year performance (below), FIW's low point in its 52 week range is $30.16 per share, with $35.32 as the 52 week high point — that compares with a last trade of $31.93. First Trust ISE Water Index Fund shares are currently trading off about 0.4% on the day.