Living Water International is the water aid organization working with Advent Conspiracy. They released a Prayer Guide recently. It offers statistics about the world water crisis as well as suggestions about how to pray. Here’s a copy online. This is an excerpt:

Water is mentioned in the first chapter of Genesis, the last chapter of Revelation and several hundred times throughout Scripture. Water is often used in scripture to communicate God’s character and provision for all creation and for every living creature. Without water, there is no life—spiritually or physically.
As you engage in strategic intercession for the water needs of the world, the following guidelines may be a helpful focus for your prayer.

Worship – Effective prayer begins when we worship the Lord Jesus in Spirit and in Truth. True worship enables us to walk in purity and holiness and be effective intercessors.
Adoration – As we engage in times of adoration and acknowledgment of God, He will direct our paths and direct our thoughts and attention to those things nearest His heart.
Thanksgiving – A heart of gratitude will enable us to recognize that He controls all things and that He is working everything according to His purposes.
Edification - God will edify His people as we seek first His kingdom and His righteousness. He has promised to show Himself strong on our behalf as we have pure hearts before Him.
Repentance – As we receive God’s Word, confess and repent of our sins, He will forgive our sins and cleanse us from all unrighteousness and renew our hearts.

Check out their site.