Keeping water at arms reach is probably what helps the most. But I read a few things when I was pregnant that really helped me with upping my water intake.

1. Have water at bedside table. When you wake in the middle of the night have a few big gulps before going back to sleep.

2. Have a drinking vessel with a straw. Something about moving head down or up making drinking difficult, a straw might help.

And of course, not everyone needs two litres of water a day. Hope it helps!