Make your mouth water

Example

Look at the buffet! It makes my mouth water

Keep one's head above water

Example

Despite the scandals and accidents  the team has managed to keep their head above water so far

Water under the bridge

Example

Do not bear a grudge against Helene the matter is water under the bridge by now

Dead in the water

Example

The company is in a recession, the project for the advertising campaign is dead in the water

First water

Example

The diamonds in that showcase are definetely of the first water

Pour oil on troubled waters

Example

The discussion was going out of control, when Mary managed to pour oil on troubled waters wisely

Not to hold water

Example

I called to order Peter and asked for an explanation but his version of the facts didn't hold water

Does not hold water

Example

The subject to be discussed does not hold water, it is too theoretical

In dire straits - hot water

Example

Economic policy of the third millennium is in dire straits

Come hell or high water

Example

I am not going to retreat my decision come hell or high water

In deep water - water up to the ears

Example

The public debt is unsustainable, Greece is in deep water (has water up to his ears)

Water off a duck's back

Example

These unnecessary criticisms is like water off a duck's back

Take to like a duck to water - on the fly

Example

He's taken to his new difficult job like a duck to water

A fish out of water

Example

I do not feel comfortable here. I am like a fish out of water.