There are many ways to bless water. You may think it’s easier to steal it from your local church, but I’m afraid I can’t advocate doing such a thing.
These Methods won’t include any specific incantations — I encourage you to write your own!
Fill a cup or container with bottled or tap water. I suggest tap. Take some salt and sprinkle it widdershins (that’s deosil for you Pagans off in the southern hemisphere) into the water. Speak an incantation as you do this. Congratulations, you water is now blessed.
Fill a container with bottled or tap water. I suggest tap. Seal the container and leave it out overnight during a full moon, whether it be at the window in your home or outside your house. Whether you say an incantation is completely up to you. Come get it the next morning.
A combination of methods one and two. Fill a contained with bottled or tap water. Again, I suggest tap. Sprinkle salt into the water widdershins (deosil for those of you south of the equator). Say an incantation as you do this. Seal the container and leave it out overnight during a full moon, whether it be at the window in your home or outside your house. Come get it the next morning.
You may choose to just say an incantation over the water and consider it blessed, but I feel that at least any one of these steps is necessary to bless water.