Wait for a raindrop in the drought: When someone is waiting for a raindrop in the drought, they are waiting or hoping for something that is extremely unlikely to happen.

Waiting in the wings: If someone is waiting in the wings, or in the wings, they are in the background, but nearby, ready to act on short notice.

Wake-up call: A wake-up call is a warning of a threat or a challenge, especially when it means that people will have to change their behaviour to meet it.

Walk a fine line: If you have to walk a fine line, you have to be very careful not to annoy or anger people or groups that are competing. ('Walk a thin line' is an alternative).

Walk a mile in my shoes: This idiom means that you should try to understand someone before criticizing them.

Walk a tight rope: If you walk a tightrope, you have to be very careful not to annoy or anger people who could become enemies.

Walk in the park: An undertaking that is easy is a walk in the park. The opposite is also true - "no walk in the park".

Walk on eggshells: If you have to walk on eggshells when with someone, you have to be very careful because they get angry or offended very easily.('Walk on eggs' is also used.)

Walk the green mile: Someone or something that is walking the green mile is heading towards the inevitable.

Walk the plank: If someone walks the plank, they are going toward their own destruction or downfall.

Walking encyclopedia: A very knowledgeable person is a walking encyclopedia.

Walking on air: If you are walking on air, you are so happy that you feel as if you could float.

Walking on broken glass: When a person is punished for something. e.g. 'She had me walking on broken glass.'

Walking time-bomb: A person whose behaviour is erratic and totally unpredictable is a walking time-bomb.

War chest: A war chest is a fund that can be used to finance a campaign like and election or for use in emergencies or unexpected times of difficulty.

War of words: A war of words is a bitter argument between people or organisations, etc.

Warm the cockles of your heart: If something warms the cockles of your heart, it makes you feel happy.

Warpath: If someone is on the warpath, they are very angry about something and will do anything to get things sorted the way they want.

Warts and all: If you like someone warts and all, you like them with all their faults.

Wash your hands of something: If you wash your hands of something, you disassociate yourself and accept no responsibility for what will happen.

Waste not, want not: If you don't waste things, you are less likely to end up lacking.

Waste of skin: If a person is referred to as a 'waste of skin', it means he is not worth very much.

Watch your back: If someone is after your job, or wants to harm you in any way, you need to "watch your back" to metaphorically see what is going on behind you.

Watch your six: This idiom means that you should look behind you for dangers coming that you can't see.

Watching paint dry: If something is like watching paint dry, it is really boring.

Water off a duck's back: If criticism or something similar is like water off a duck's back to somebody, they aren't affected by it in the slightest.

Water over the dam: If something has happened and cannot be changed, it is water over the dam.

Water under the bridge: If something belongs to the past and isn't important or troubling any more, it is water under the bridge.

Watery grave: When someone is in a watery grave, they have drowned.

Way to go: Another way of saying well done.

Weak at the knees: To be nervous or so emotional that you start to get shaky and can’t seem to stand on your feet.

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Left is Right