It's impossible to overstate our dependence on water. Even though roughly 70% of the earth is covered by water, only a tiny fraction of 1% is fresh and readily accessible to sustain over 7 billion people.

In fact, the United Nations authored a report in 2015 suggesting that the world may only have 60% of its required water by 2030, absent major global policy changes. The bottom line is that water is a precious and increasingly scarce commodity, so now might be the right time to consider adding it to your portfolio for long-term growth.

More investment advisors are recommending commodities as a dedicated asset class to hedge other assets in your overall portfolio. If you're looking at diversifying your commodities holdings to include exposure to water, you could look at individual water utility stocks if you have the time and inclination—or you could check out the emerging class of water exchange-traded funds (ETFs) to hedge your bets.

Here are three of the more prominent water ETFs for investors to consider. While had solid returns in 2019, these ETFs have also delivered stronger returns over the last five years and stand to benefit when the sector picks up. All figures are as of Jan. 14, 2020.

1. Invesco Water Resources ETF (PHO)

This is the largest and arguably the most popular water ETF, with over $1.12 billion in assets under management (AUM). Unlike other water funds, PHO is U.S.-centric, with a basket of 36 holdings that tilts toward mid- and smaller-cap companies, heavy on machinery and utilities and light on industrials.

PHO's top 10 holdings comprise almost 60% of the portfolio; Danaher Corp., Waters Corporation, and Roper Technologies are the three biggest holdings. Shares are up 10% in the last six months. The stock has posted gains over the 1-year, 3-year, and 5-year periods, rising 33%, 17%, and 10%, respectively. 

2. Invesco Global Water ETF (PIO)

The PIO portfolio, with over $200 million in assets under management, tracks the Nasdaq OMX Global Water Index and focuses on global companies that create products for water conservation and purification. As you might expect, the portfolio is heavily tilted toward industrials and utilities, with a strong preference for large-cap growth and value.

The portfolio is pretty concentrated as well, with the top 10 holdings accounting for almost 55% of its assets. There are 43 holdings. Top names include Danaher Corporation, Geberit, and Ecolab Inc.

While PHO is preferred by many investors, PIO is a good play for investors with confidence in the fund's top holdings. Shares are up 11% in the last six months. Longer-term the results are better. The fund has delivered one-, three- and five-year annualized returns of 30%, 15%, and 8%, respectively. 

3. Invesco S&P Global Water ETF (CGW)

As the name suggests, this fund tracks the S&P Global Water Index and invests in companies of all market caps that stand to benefit from the increased demand for water, including water quality and delivery infrastructure.

Although CGW has global exposure, it is heavily weighted to the U.S. (roughly 48% of its holdings) and the U.K. (roughly 13%). There are currently 51 companies in the fund's basket, with the top 10 holdings accounting for over 52% of its overall holdings; American Water Works, Xylem, and Geberit are the three biggest holdings.

The company has nearly $721 million in assets under management. So far in 2019, shares are little changed, down 0.90%. The fund has delivered one-, three- and five-year annualized returns of 30%, 15%, and 10%, respectively.