The Difference Between War and Conflict

At the beginning of this blog I raised the question if there will be war over water one day. This question implies that up to now there haven't been any wars over water. Nevertheless water war is a common term. I think it is important in this context to distinguish between the terms. When can one talk about war? What is the difference between a war and an (armed) conflict? It is important to know this to rate disputes about water.

The free dictionary defines “war” as:

a. A state of open, armed, often prolonged conflict carried on between nations, states, or parties.

b. The period of such conflict. 
c. The techniques and procedures of war; military science.

When I type in “armed conflict” the dictionary redirects me to “war”.

The site also defines “conflict” as:

1. A state of open, often prolonged fighting; a battle or war.
2. A state of disharmony between incompatible or antithetical persons, ideas, or interests; a clash

It is difficult to see the differences between war and conflict within these definitions. A war is armed. A conflict maybe not? But a conflict can be war.

I am wondering what are right evidences to measure war. The number of people killed? The weapon used? The period of time?