To your example. During the US housing price bubble (so called) that deflated 08; it was generally much cheaper to rent. So a user did not necessarily have to buy a house. And when you purchase real estate far beyond what is needed, then obviously you will have to rent because you can't occupy it all by yourself. The true price of living hasn't changed just because people are overvaluing real estate.

Consider water. Say a speculator drives the price way up in the sky to the extent that ordinary people are affected. What will said speculator do with these contracts? Either she will sell them (and the price rebounds), or she will be stuck with tons of water which is burdensome and incurs costs to store. So clearly she will want to sell this water and at that point be subject to the market demand for it.

In other words, undue speculation drives you out of business.

Now, regarding this future contract it is financially settled based on the actual index value of what water costs. So it's not capable of being driven by silly speculation at all.