Sustainability with natural resources
A sustainable approach means to use resources without over usage. No excessive usage of water or energy or raw materials. But what is sustainable and what is not is no always easy to understand. As where stops normal consumption and where starts over consumption?
When you buy something you rarely know what resources have been used and which amount. You have not much information and definition is difficult.
As less as possible
As there is no information, you consume differently. Buy less and refuse to buy from time to time. Like this you lower your overall consumption and assure a sustainability.