Energy (15)

Amazons start with 50 mana and 15 energy; they gain 1.5 mana per clvl. Every point of energy adds 1.5 mana. Unlike life, mana refills over time: the more mana you have, the more mana you regenerate per second. According to Librarian's FAQtoids in DiabloII - Lord of Destruction, Patch 1.1x, it takes two minutes for an unmodified mana bulb to go from empty to full, regardless of how much mana is needed to completely fill the bulb. There are many formulae to show how mana regeneration items can influence this, but they're not necessary for a bowazon player to know.

Mana will always be a problem for the bowazon: while her attacks have a relatively low mana cost, she simply doesn't have the kind of mana reserves needed to use them non-stop (at first). This is immediately noticeable when she starts using skills like Multiple Shot or Cold Arrow, as she'll completely drain her mana reserves within a few shots. More glaring examples include the high-level valkyrie and high-level elemental arrows (though in both cases, the potential payoff is worth far more than the initial cost). However problematic this may be, it is not a wise idea to invest in Energy. There are multiple reasons for this.

It is far more advantageous to boost the bowazon's mana through equipment than actually investing in energy, because 1.5 mana per point placed into energy is an incredibly bad investment, and mana-boosting items aren't that hard to find. For example, a perfect sapphire gives +38 mana, the equivalent of around 25 points of Energy. Another workaround involves "Mana per Kill" items, which work wonderfully when used with elemental skills with their AOE and high damage...and lack of leech.

For most bowazons, though, mana stops being a concern when she is able to safely leech mana with the proper equipment — this usually occurs around level 25~30, when she's able to start using exceptional-grade weaponry. While she won't be able to spam Strafe or Multiple Shot non-stop, she'll be able to mostly depend on mana leech to keep her reserves up. In short, the more damage your bowazon does and the more mana leech she uses, the more mana she can afford to burn: a bowazon with fairly high damage and around 7% mana leech can safely strafe non-stop in Hell (assuming sufficient AR).

Where can I get extra energy?

Equipment:

Rare rings, magical helms: +1-15 energy.

Rare amulets, circlets, magical rings: +16-20 energy.

Magical amulets, circlets: +21-30 energy.

Various unique, set, and rune word items give varying amounts of energy.

Sockets:

Rare jewels of knowledge: +4-9 energy.

Lum rune: +10 energy when socketed in anything.

Charms:

Annihilus small charm: +10-20 energy.

Hellfire Torch large charm: +10-20 energy.

Where can I get extra mana?

Equipment:

Rare body armor, boots, gloves: +1-40 mana.

Rare amulets, circlets, rings: +41-60 mana.

Magical amulets, circlets, rings: +61-120 mana.

Magical amulets, circlets: Memory prefix (+[0.5/clvl] mana).

Magical circlets: Elephant prefix (+[0.25/clvl] mana & mana).

Various unique, set, and rune word items give varying amounts of mana.

Sockets:

Sapphires of varying quality in helms and armor: +10-38 mana.

Charms:

Small charms: +1-17 mana.

Large charms: +2-34 mana.

Grand charms: +3-59 mana.

It's come to my attention that one of the ladder-only rune words, Insight, offers a slvl-12~17 Meditation aura (575~675% mana regeneration) when equipped; it can be placed in a staff or a polearm. The required runes are relatively easy to obtain (Ral + Tir + Tal + Sol), so any bowazon would be well-advised to give this to an Act 2 hireling as soon as possible. This is by far the best option for mana regeneration for the LOD amazon: even with base energy, a bowazon can refill an empty mana orb in under 10 seconds with this aura active. (Of course, this has the unfortunate side effect of making your bowazon incredibly dependent on an aggressive, brainless, and worst of all, erratic minion to be a mana battery!)