EPANET Errors Status Report

!Hello:

I am a new user to EPANET. I am having trouble where I am getting negative pressure at my nodes.

I have my pump curves in, and I am just unsure of how to go at it. I placed the necessary elevations at the nodes, as well as the pipe lengths and diameters. My question is, do I need a base demand for each one of the nodes?

Could I have it be at zero?

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