The Norwegian drinks water, the Chinese owns the zebra.

Let's mark everything from 1 to 5, 1 being the leftest.
From clues 10 and 15, The Norwegian is at 1, house 2 is blue. From clues 2 and 6, the Norwegian cannot have a red, green or ivory house either, so the Norwegian has yellow. From clues 8 and 12, the Norwegian also has roses and the horse is kept at 2. Now from clue 6, ivory/green are either 3/4 or 4/5. From clues 4 and 9, there're only two places to fit clue 13, but only 1 that also fit clue 5. That left water, the only drink missing, to the Norwegian.

Now we have:
nationalities
color
pet
drinks
flowers

N U E ? ?
Y B R I G
W T M O C
? H ? ? ?
R ? ? L ?

or

N U ? ? E
Y B I G R
W T M C O
? H ? ? ?
R ? ? ? L

If the first configuration is true, from clue 14, the Chinese and the gardenias must be at 5. From clue 3, the Spaniard and the dog must be at 4. Now from clue 7, the geranium and the snails must be at 3. The only space to fit clue 11 is fox at 1 and marigolds at 2. So the last blank, the zebra, is at 5, owned by the Chinese:

N U E S C
Y B R I G
W T M O C
F H S D Z
R M G L Ga

This satisfies every requirement.

If the second configuration is true, clues 14, 3 and 7 cannot be met at the same time.