FIW holds 36 of the largest US-listed water companies, ranked by market cap and weighted equally within five tiers. Companies of any market capitalization that derive revenue from the potable and wastewater industry are selected. In addition, its tiered equal-weighting scheme boosts the weight of small- and micro-cap companies, hence, reducing concentration. FIW changed its name from First Trust ISE Water Index Fund to First Trust Water ETF on December 14, 2016, which had no impact to FIW's investment strategy. The index is rebalanced and reconstituted semi-annually.