Gender?

Guten tag I'm new here but really loving this program. I seem to have confused myself a little while trying to learn genders of nouns. Yesterday I learnt in Part one of gender that a masculine noun uses 'DER'... however today part 2, Glass Wasser is 'DAS WASSER'. As Wasser ends in ER, I thought it was Masculine? Perhaps I've just managed to pick an exception? Thank you for any help you can give. I'm trying to learn with my 13 year old son to make it easier for him at school too so need to make sure I'm right. Claire.

Try the Language & Culture Lessons starting with this one: http://members.rocketlanguages.com/lessons/59 Also, here are two tools to help you check your understanding. 1) Rocket Langauges My Vocab: Highlight the word Wasser in the lesson. Normally a My Vocab tool comes up. Use it to check for similar words. Save the words you like the most. 2) Dict CC http://www.dict.cc/?s=Wasser Several good things about this tool: 1) You can easily type your own word on the end to create your own links http://www.dict.cc/?s= 2) They have an ipad app 3) They have volunteers that record the audio for may of the words 4) They have conjugation tables for verbs http://www.dict.cc/deutsch/fahren.html -Jason