One of the original (excellent) gravity water supply system design manuals, with specific focus on humanitarian efforts. Rules of thumb, hand calculation examples – great material worth saving to reference for the remainder of your career. It’s referred to the “Jordan manual”, and I recommend that these basics are understood before EPANET is attempted.
To learn hydraulic theory fast, jump into chapters 6 through 8. Own this material – memorize, flashcards, whatever it takes. This material should be second nature to you, if you plan to design a gravity water supply system.