Science Project Help - Water Purification

[Ra1]

Hi,
This year I've been wanting to do my project on water purification and how water can be reused sustainably. My first idea was how extra weight on a skateboard can affect its speed, but I think it's too basic? For ideas I've been thinking of maybe seeing how to reuse water that you wash dishes with or collecting moisture from showers, or just in general an easier way to purify water. The thing is, I need quantitative data and I'm not sure how to organise these experiments. If possible, some ideas or help on this would be really appreciated. Thank you!