At a temporary mosque non-Muslims (Christians) may enter to get water in soiled containers. Here more than 1000 Muslims make Wudu using the same water. What action do you advise?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

As for the ruling of allowing a non-Muslim to enter the mosque, please refer to Fataawa 82236, 81478, and 81644.

With regard to using water, if there is much water that cannot be influenced by this recipient, or if the water is little but the recipient does not contain any impurities, then there is no harm that this man takes some of the water which Muslims use for ablution. The Prophet clarified that the Muslim is rewarded for giving animals to drink. The Prophet said: “A man was walking on a road when he became very thirsty. He found a well and went into it and drank and came out. There was a dog panting and eating mud out of thirst. The man said, 'This dog has become as thirsty as I was.' He went down into the well and filled his shoe and then held it in his mouth until he climbed out and gave the dog water to drink. Allah thanked him for it and forgave him.” They said, “Messenger of Allah, do we have a reward for taking care of beasts?” He said, “There is a reward in every living being.” [Al-Bukhari]

So, there is no doubt that the reward is greater if the drink is given to a human being, even a non-Muslim. This might reconcile his heart to Islam and might make him friendly towards Islam and Muslims.

But if there is little water and the container he uses has some impurity that could stain or spoil the water, then, in this case, he should be hindered from entering his receptacle into this water and should be given the water he needs by other means. But he should not be prevented from taking some water as we explained earlier.

Allah knows best.