If you are wasteful, you are not careful about saving things or using them efficiently; you waste a lot.

Example uses:

You only took a few bites of your food and now you’re going to throw it away? You’re being wasteful.

Wasteful employees can cost a company a lot of money.

You shouldn’t be wasteful.

Similar ways to express the same meaning:

Uneconomical

Lavish

Extravagant