I happened to buy this Solar Shower for $6 at Walmart the other day, to put in my preparedness supplies. Coincidentally, the next day we lost our water for 24 hours. I ended up using the solar shower (I hung it inside my bathroom shower), and it was wonderful. In fact, the water got so hot I had to add a bunch of cold water to it because it was burning me.
I decided to go back to Walmart and buy several more, to give to all my kids. I went back and in three days, the price had gone up from $6 to $6.80. These are plastic, so they are made of petroleum, so they are only going to get more expensive.
The box says that these are not food grade plastic, so you are not supposed to drink the water from them. But I am going to buy several for myself, so that when we don't have power we will have hot water for doing dishes and for doing laundry.