Water is life! Investments in water are typically split between 'Industrials', like pipes, pumps, filters, and faucets, and 'Utilities', who make profit selling water through the taps. These investments do not include bottled water or massive hydro-electric dams.
As the climate continues to change, more pressure will be put on the world's water systems. This sector is expected to grow as 1) rich countries replace aging infrastructure; and 2) emerging economies keep building out new water systems.
For more information, read this blog post I wrote: Why Invest in Water