Good question!
Before we can talk about "estimated cost", we need to take a closer look at the details.
#1 - Pool Chemicals
Pool water treatment will be your biggest expense.
Swimming pools require pool chemicals and pool chemicals need to be purchased.
If we are going back to the "family pet" analogy, let's consider pool chemicals similar to pet food. A necessary expense to ensure a healthy pool.
There are a lot of things to consider when it comes to pools. Weather, environment, and bather load, to name a few. The amount of money that you will spend will be adjusted by these factors. That being said, in an effort to establish a sort of "budget" for you, we've put together a little chart to help you out.
The chart above shows the estimated cost using a chlorine based system of chemicals on varying pool sizes. This chart coincides with the standard treatment methods widely used for pool water treatment.
#2 - Equipment Upkeep
Aside from chemicals, you will have to consider the cost of other upkeep.
As a pool owner, you should be aware of one simple fact:
Chlorine + Sun = Damage to Plastic and Vinyl.
Unfortunately, many of the things used in and around a pool are plastic and vinyl. As the pool gets older, expect that there will be a need for replacement for these things.
Filter hoses break, o-rings fall apart, and liners eventually get faded and brittle.
In the long haul, you will need to plan and allow for other needs, such as, pump replacment, filter repairs, and the addition of or replacement of other accessories.
You can save money by putting cleaning tools away when you are done with them, storing covers in the shade, and by placing the filter system out of direct sun all day long.