The world’s safe water supply is a concern to many individuals, groups, nations, and continents. As well it should be. According to the World Health Organization, 663 million people on earth lack access to safe water. The World Economic Forum claims that the water crisis is the #1 global risk, based on its impact to society. Therefore, investment in water resources and infrastructure not only makes good sense, but also is vital and necessary.

Everything in economics usually comes down to supply and demand. The demand for clean and safe water outstrips the supply. However, if there were ever an ETF category where supply outstripped demand, it would have to be water ETFs. The law of supply and demand regarding investment vehicles is at odds with the supply and demand of the underlying resource.

I bring this up because a new water ETF was listed for trading in the U.S. today. The Tortoise Water Fund (TBLU) “provides access to the water infrastructure, management and treatment companies that appear poised to benefit from the expected and much needed investment in rebuilding existing infrastructure, constructing new infrastructure and better managing this vital, but finite resource.”

On the surface, this sounds like a good idea for a new ETF. However, you might not be aware that there is already a water ETF available to U.S. investors. In fact, there are now six of them listed on U.S. exchanges. The first one arrived in 2005, three more have been around for nearly 10 years, and two have come to market in the past six months.

Here are the six water ETFs, listed by launch date:

• PowerShares Water Resources (PHO), launched 12/6/2005, tracks the Nasdaq OMX US Water Index, a modified equal-dollar weighted benchmark of U.S. exchange-listed companies and ADRs that create products designed to conserve and purify water for homes, businesses, and industries. It holds 37 stocks, has $775 million in assets, and an expense ratio of 0.61%.
• First Trust Water (FIW), launched 5/11/2007, tracks the ISE Water Index, a modified market capitalization-weighted index composed of U.S. exchange-listed companies and ADRs that derive a substantial portion of their revenues from the potable and wastewater industry. It holds 36 stocks, has $250 million in assets, and an expense ratio of 0.57%.
• Guggenheim S&P Global Water (CGW), launched 5/14/2007, tracks the S&P Global Water Index, which selects 25 water utilities and infrastructure companies along with 25 water equipment and materials companies. Its top country allocations included the U.S. 45%, U.K. 15%, Switzerland 9%, France 7%, and Hong Kong 7%. It has $475 million in assets and an expense ratio of 0.64%.
• PowerShares Global Water Resources (PIO), launched 6/13/2007, tracks the Nasdaq OMX Global Water Index, making it a global version of PHO above. Its top country allocations included the U.S. 37%, Switzerland 16%, U.K. 15%, France 11%, and Japan 6%. It holds 39 stocks, has $185 million in assets, and an expense ratio of 0.76%.
• Summit Water Infrastructure Multifactor (WTRX), launched 8/9/2016, tracks the Summit Zacks Global Water Index of publicly listed U.S. and international companies with a significant portion of their business activities dedicated to the global water industry. It uses a three-factor fundamental model that has provided strong historical indicators of the long-term performance of water equities. Its top country allocations included the U.S. 18%, U.K. 15%, Switzerland 10%, China 8%, and Japan 7%. It holds 50 stocks, has only $4 million in assets, and an expense ratio of 0.80%.
• Tortoise Water Fund (TBLU), launched 2/15/2017, tracks the Tortoise Water Index, which follows a proprietary rules-based methodology using fundamental weighting. The underlying index consists of 34 companies, with single issuer exposure capped at 7.5%. It is global in nature, but the individual country exposure is unknown at this time. It holds 34 stocks, has an estimated $2.5 million in assets, and an expense ratio of 0.40%.

Interestingly, asset size seems to be a function of age rather than performance or other criteria. With the exception of Guggenheim S&P Global Water (CGW), which has more assets than the three-day older First Trust Water (FIW), longer time on the market has equated to more assets. While all four of the ETFs that have been around since 2007 are healthy in terms of assets, with $185 million or more, none of them has cracked the $1 billion barrier.

Expense ratios range from a low of 0.40% to 0.80%, but the differences should not be deciding factor with these funds. A global versus U.S. focus might be an important data point for someone looking to buy a water ETF, but for most investors looking to buy, the decision likely comes down to performance.

Fortunately, there is more than 9.5 years of performance for the four entrenched products, and reviewing that history produces a clear winner. The performance of the First Trust Water ETF (FIW) crushes the competition across nearly every time interval. Since June 14, 2007, FIW has returned 8.0% annualized versus 4.2% for CGW, 3.0% for PHO, and -0.1% for PIO. Additionally, FIW has accomplished this task with lower volatility than two of the other three. Over the past year, it has beat its competitors by 9.4% to 24.6%.

I do not own a water ETF today, but if I were inclined to do so, my choice would be the First Trust Water ETF (FIW). Its performance advantage is nothing new. It has led the group in performance consistently since 2007, which makes one wonder why it is only the third largest among the four water ETFs with long-term history. It has even outperformed the S&P 500 Index in dramatic fashion.

No matter how great the need for investments in the world’s safe water supply, there is clearly not a large demand for water ETFs at this time. Not enough to support six of them in my opinion, and some will probably fall by the wayside eventually. If shareholders start looking at their performance versus the competition, then “eventually” may come sooner. The two newcomers certainly have a tough road ahead to avoid becoming just another ETF fatality statistic.