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Should You Fill Your Pool with Well Water? (Honest Answer)

Are you thinking about using well water to fill your pool?

Concerned it may be too difficult to balance, make your water cloudy, or cause your pool surfaces to stain?

This article will break down everything you need to know about filling your pool with well water, whether or not it’s a good idea, and how best to treat it.

Why Use Well Water in a Pool?

There are two good reasons to consider using well water to fill your swimming pool, or even just to top it up:

  • It’s free to use. Since there’s no middle man metering your usage, you can take as much water from a well as you need without paying a cent, which makes it a great way to cut the running costs of owning a pool.
  • It’s accessible. Wells are normally found outdoors, as are residential pools. Assuming you’ve got a long enough hose to bridge the gap, you can’t ask for a more convenient setup, can you?

While these are both valid reasons, you also have to be aware of some of the potential complications of using this water source to fill a pool.

And that brings us to the next question…

Can You Fill a Pool with Well Water?

It depends.

Well water isn’t objectively worse than city water, or water from any other source for that matter.

Regardless of where it comes from, the most important thing to know before filling a swimming pool is what’s dissolved in that water— or, more specifically, how saturated the water is.

Since well water comes from the ground, it tends to absorb minerals in the soil that make it high in saturation. As a result, it’s far more likely to be high in minerals like iron, copper, manganese, and calcium.

Whether or not it’s safe to use well water in a pool depends on how much of these minerals are dissolved in the water, and the only way to know for sure is by testing it first.

Why is Saturated Water a Problem for Pools?

High metal content is the most common issue when it comes to using well water to fill a swimming pool.

In particular, well water usually has high concentrations of iron, copper, and manganese. When these metals become oxidized in your pool, it can cause some nasty metal staining on your surfaces and equipment.

Did you know? Metal stains are usually deep shades of brown, green, or purple depending on which metal is the culprit. While metal stains are more common with fiberglass pools, plaster pools, and even vinyl pools can get them too.

High levels of iron will also turn your water a murky brown after adding chlorine; a problem that will be recurring until you eventually remove enough iron.

High metal content can also create more work when it comes to balancing the water. Since oxidizing metals use up your chlorine, you may require more chlorine than usual to reach the ideal sanitation level — also known as “chlorine demand”.

Finally, well water also tends to be high in calcium, which makes what’s often described as “hard water”.

A high calcium hardness level will not only make your water cloudy but will also deposit excess calcium around your pool surfaces and equipment in the form of calcium scale; a white, chalky substance that’s a pain to remove.

How Do You Test Well Water?

Most pool testing kits don’t check for metals, and only some will check for calcium hardness.

While you can invest in a kit that checks for iron and copper levels, it’s usually an additional purchase, so it might make more financial sense to have your local pool store run the tests instead.

Now, if you do have a test kit that checks for calcium hardness, it’s worth testing this yourself since it’s unlikely pool store testing will be any more accurate – assuming you’re doing it correctly.

If don’t have a suitable test kit for this either, you may as well have the store check the calcium content as well.

Note: Pool stores will often try to sell you products you don’t necessarily need, especially after running a test for you. Stand your ground and trust your research.

How Much Metal or Calcium Is Too Much?

Most water contains traces of metals and a small amount isn’t going to cause any issues in a well-maintained swimming pool.

For iron and copper, you don’t want anything over 0.3 parts per million (ppm) as this can lead to stained surfaces or murky brown/cloudy water after chlorination.

Manganese isn’t nearly as common in well water, but anything over 0.1 ppm should be concerning for the same reasons.

While there are ways to filter metal out of well water, you should still use these numbers as the upper limit during testing because, in reality, you’ll only ever remove a percentage of metal.

Calcium is much less of a problem because you actually need this mineral for balanced pool water. Too little, and your water becomes corrosive as it tries to seek out calcium wherever it can.

Ideally, you want to see a calcium level between 200 and 400 ppm, with somewhere close to 300 ppm being the most optimal.

Again, there are ways to reduce calcium in well water but this often requires more money and effort than it’s worth. If your well water tests well over 400 ppm, just give it a pass.

Can You Use Well Water to Top Off a Pool?

Pools lose water for various reasons, including leakages, splashing, evaporation, or backwashing.

Whatever the reason, when the water level gets too low, it should be replaced in order to keep the level optimal and your filtration system running efficiently.

The question is, can you use well water to top up your pool?

Well, if the mineral content is within the acceptable limits (see above), there’s no harm in using it for regular top-ups just as there’s no harm in using it to fill your entire pool.

However, if the mineral content is NOT within acceptable limits, even using it to top off your pool is a bad idea in the long term. Even though a small amount of saturated well water will be heavily diluted after adding it to your pool, when that water evaporates, it leaves those minerals behind

As you continue to replace the lost water, mineral content continues to build up until it eventually exceeds the acceptable limit. This happens slowly over time, but it WILL catch up with you.

How Do You Filter Well Water to Remove Metals and Calcium?

It doesn’t matter what pool filter you have, neither cartridge, sand, or DE filters capable of filtering out metal ions or calcium particles; they’re simply too small.

While it’s not easy to treat well water for metals and calcium, there are ways to remove a considerable amount of this content from the water, especially if you’re using multiple methods in combination.

Note: For metals, in particular, it’s still worth filtering your water even if your test results show a low enough reading. The lower you can get it, the less chance you’ll have to deal with staining in the future.

Use a Metal Trap to Remove Some Metal

Pre-filtering the well water as it enters your pool is by far the easiest way to remove metals (with no effect on calcium), even if it’s not the most effective.

Simply attach a metal trap to the end of your hose and wait for your pool to fill up as usual. As the water passes through the filter attachment and into your pool, some of the iron, copper, and manganese ions will be caught in the trap.

It’s hard to say exactly how much metal will be filtered out as reports vary, but some pool owners have seen up to a 50% reduction.

These attachments do have a limit in terms of how much water they can filter before needing to be replaced, so be sure to check the capacity (in gallons) to make sure it covers you.

You will also need to run the hose at a lower flow rate to ensure maximum filtration, which may mean waiting several days to fill a large pool from empty.

Use a Metal Sequestrant to “Disable” Metals

Metal sequesters don’t actually remove metal from your water but they do bind to metals which effectively “disables” them. Think of it like being bear-hugged while trying to swim.

While the metals still remain in the pool, this process prevents them from clouding your water or staining your pool surfaces for as long as you continue to use sequestrant.

All you need to do is pour the instructed amount of liquid solution into your pool water (before adding chlorine), and your pool will have temporary immunity from the consequences of high metal content.

While you can use this regularly, most sequestrants are phosphate-based. This means long-term use will significantly increase the phosphates level in your water, which may make your pool more prone to algae.

Pro tip: Despite the name, metal sequestrant also has the same (but often lesser) effect on the calcium in your water.

Drain and Refill to Lower Metals and Calcium

The most effective approach is almost always a drain and refill, even if it’s just to partially dilute the concentration of minerals.

Assuming the refill water is low in metal and calcium to counter the high content in your pool, this process should bring your water within the acceptable limits for both.

Pro tip: If your metals are too high but your calcium level is ideal, don’t be discouraged from using soft water to refill your pool. You can always bring the calcium level back up by adding calcium chloride to your water.

It doesn’t matter if you use city water, well water, or even trucked in water, just make sure the mineral content is below the acceptable limits.

Use Reverse Osmosis to Remove Everything

Reverse osmosis pushes water through a “semipermeable membrane” at high pressure. This membrane allows water to pass through but filters out (nearly) everything else.

It’s basically a filter on steroids.

This can be used to remove almost all total dissolved solids from pool water, including minerals and chemical compounds that would otherwise be very difficult to remove.

That includes minerals like calcium and metals like iron, copper, and manganese — however, water with particularly high metal content can clog up the membrane so it’s better used to reduce high calcium content.

The biggest downside to this approach is that it consumes a lot of water in the process. In fact, you can expect more than half of your pool water to go to waste which means a partial refilling is always required.

If you wish to go this route, you’ll need to find a local provider and expect to pay a few hundred dollars for the service. This can be easier said than done if you don’t live in an area with hard water.

Answer: Use Well Water With Caution

Well water can be used in swimming pools provided it isn’t too saturated, and you can only know by testing.

If you’ve tested the water and the numbers make sense, go ahead and fill your pool; otherwise, using well water can be more trouble than it’s worth.

Remember, it doesn’t matter how much money you save on water if you have to spend hundreds of dollars treating and balancing it.

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