You can omit the OM when doing many after the first. Visualize the mother nature of the spirit of earth.
This mantra is to the mother nature asking her for rain. Mother of Sipe Gyalmo who controls all the five elements, please give us some water into the area as people need. Help cool down the wind, bring moisture into the area. Please help. We can blow a conch, bless pills, and do Naga mantras too. Place the blessing pills into the springs and natural water so the Nagas will be happy and bring rain. If we cannot do this, we can just do the mantra to bring rain. We connect to the Nagas as we do this mantra meditation. And we ask the Nagas for help. We can invite the bell as we do.