[header] How to use solar energy to heat a pool [title] Use a long, dark-colored hose to fill up your pool. [step] The longer it takes for water to make its way through the hose and into your pool, the warmer that water will be. While fifty feet of hose is generally sufficient, additional length means the water will have even more time to warm up. 
The added surface area of the hose collects more heat, as well. If you use a dark-colored hose, the water can get even warmer because dark colors absorb more solar energy.