The rent you pay to De Key is including the use of water, electricity and internet. It does not include water and waste taxes you might have to pay as a citizen of Amsterdam.
Usually residents who rent a private room with private or shared facilities. Sometime also one of the 2 residents who rent a shared room can receive an invoice.
The main reason why these taxes are not included in the rent is because most students can apply and do receive a remission/exemption (in Dutch this is called 'kwijtschelding').
It depends on your personal finacial situation but in general these are the two main criteria:
Your monthly income is below € 982,79.
Your private capital (savings) is not more than € 2269,00.
You can call the City of Amsterdam below (Mon-Fri from 8 AM till 6 PM) of look on one of the links.
Do as much as you can yourself, Google Translate and your smartphone make these things possible nowadays. The RA's, Student Caretakers or a Dutch neighbour can do a final check when you ask them politely.