Education. There are a number of initiatives that have been undertaken by NGO's to provide training and skills development for farmers and those in the agriculture and animal husbandry sectors to identity crops and livestock that are the most drought resistant and suitable for a specific regions climate and weather. Given the significant amount of water consumption in the agricultural and industrial sectors I would think that education and awareness (supported by Government backed training and investment initiatives) is likely to have the biggest (and least expensive) positive impact on global water security.
somewhere in the middle east or south america or wherever they pump oil out of the planet and send it on the other side of the globe ... water is already outside of the planet and easy to pickup ... if they can send entire train underground from France to England ... why not with some part of huge river like the Mississippi or other ... and send it in the area where water in a need ? ...