While the pump and filter (and more precisely, a properly-sized pump and filter) are conceivably the most important pieces of safety equipment, without question, safety equipment is the most important pool equipment. While your safety equipment may - and hopefully will - sit idle (yet visible) all pool season, it will be of the utmost importance if it is ever needed.
As a pool owner, you should definitely own a safety hook as your primary piece of pool safety equipment, which is a sturdy one-piece telepole (at least 12' long). The safety hook must be permanently adhered to the one-piece telepole with stainless steel hardware.
As back-up safety equipment, you should also own a life ring with an attached life rope (at least 30' long). A troubled swimmer can hold onto the ring, which is like a buoy, while somebody pulls in that troubled swimmer to safety with the rope.
This safety equipment should be kept in the same place in the pool area so that everybody in the family, as well as friends, neighbors, and everybody who uses your pool knows the exact location of all safety equipment. Always make sure that your safety equipment is always located where it is supposed to be located.
The safety equipment should also be inspected often. It is recommended to check the hardware on the life hook at least twice each month (so every other week) during the pool season to make sure it is tightly secured if needed. If you also have a life ring with an attached life rope (at least 30' long), then it is also recommended to check the connection of the rope and ring at least twice each month (so also every other week) during the pool season to make sure they are secured if needed.
Every pool should also have a first-aid kit onsite.
The most valuable safety equipment is supervision. As a pool owner, it is imperative that you supervise the pool area to ensure a safe swimming environment for all swimmers and guests. It is likewise imperative that all “pool rules” are clearly defined, communicated, understood, and acknowledged by all swimmers; of course, it is just as imperative to enforce these pool rules.
You can read the Pool Manual for additional information about pool safety.
Safety first.