Well, thinking about it some more, I guess I was looking at the miracles from the wrong side. In the biography of C.T. Studd by Norman Grubb, it is related how soon after he came to China, he went on a journey to some villages in the interior, and had to walk 30-40 miles a day. He was using Chinese sandals, and his feet quickly got in bad shape, and one was infected. Quoting from Studd’s letters to his mother:

“Though I rested [the foot], it would not heal, but got very puffy, and discharged a good deal. So I asked Hogg [companion on the trip] if he would anoint me with iol in the name of the Lord, James 5:14 and 15. He hesitated at first, but we read James 5 together and prayed about it, and then he said he could see no reason against it, and did so. Since then my foot has got most rapidly better. Next day in faith I took it as being well (though it looked anything but so), and walked a good deal on it. It was much less swollen at night. I have continued to do nearly 20 miles a day on it since, with the result that it has lost all swelling, and is as fine as the sound one, and there is no discharge. I do praise the Lord for this.”

There were several other instances, of his wife being very ill after her first child, and him having bad pneumonia, which were healed in the same way. My first [indoctrinated] thought on reading about these illnesses was, there should be some medical treatment for that. Why doesn’t he look for that, instead of praying about it. Well, obviously that’s the wrong way to look at it. God is well able to arrange both sickness and health as he pleases; medicine should be just secondary to prayer, or as a means in God’s hand – not a substitute for faith in God.

Again: just because I know the molecular structure of water, and that it is much less dense than a human body, is no reason at all that Jesus shouldn’t walk on water. As a friend told me, the whole point of a miracle is that it is supernatural. God is the creator and he can work equally well within the laws of nature which he made, or outside of them.