Kids apparently relate better to feelings then facts (not sure if its true for all kids), but what worked for us at this stage was for me to explain to my son that I saw him do XYZ (whatever you know) and how it makes me feel when he does not tell the truth. I would tell him that it makes me sad, or angry, or breaks my heart, whatever was true for me at the time.
So basically I would say that it really makes me sad that you are not telling me the truth, because I saw you kick over the dogs water. I won't be angry with you if you tell me the truth. Did you kick over the dogs water? and wait for him to admit it. Then I would say right... I'm not angry at all and thank you for telling me the truth.... don't you feel better now? And then I would explain the consequence to the action, so .... when we mess we need to be sure that we clean up after yourselves, so I'm not angry with you, but you need to clean this up, so please go get some kitchen roll and clean up. Then I would fill and jug with water and ask him to fill the dogs bowl with water. Then when all is done, praise on a good job and well done.
I tried to focus on the action and what needed to be done to fix things rather then the "lie".
This worked for us, but kids are so different it may or may not work for you.
Good luck
Hope this helped some.
PS - My son took to blaming the dog for everything (drawing on the wall, messing yoggie, you name it..... the dog did it)