broad daylight incident in Houston about 1957

We were just kids, but as avid model airplane builders we could ID every plane that flew over and also the occasional weather balloon from west Texas. We were swimming in the Briargrove subdivision swimming pool (off Westheimer Rd) one summer day in 1957 or 1958. Somebody said something like "look at that" and we saw a silver object shaped like two pointed "moon" hubcaps stuck together, slowly decending in what appeared to be a spiral, although from our vantage point it was just going back and forth. There was a tall fence along the west side of the decking around the pool and as the object descended several of us climbed up on a bench that was attached to the fence so we could see over it. I soon left the bench for the high diving board to get a prolonged view. The object was probably south-southwest from the pool. As the object got closer to the ground it passed BEHIND one of those water towers that looks like a golfball on a tee. That water tower was (probably still is) about 0.5 to 0.75 mile away so the immediate impression was that the object was 30 to 40 feet in diameter minimum, as it was not possible to tell how far behind the tower the object had passed. The object appeared to be about one third the diameter of the spherical part of the tank. The object continued it's decent until it disappeared behind a treeline. I did not believe in UFO's at the time. We discussed the matter and concluded that if it was a UFO we would read about it in the paper the next day, but no story appeared. I think there were about 8 or 10 people at the pool that day. The only person I can remember by name was my friend ((name deleted--initials "BR")) who also lived in Briargrove. The incident left a lasting impression in my mind and I can still "see" it vividly enough to be able to sketch it out.