How to Test for Phosphate in Water: 2023 Ultimate Guide

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Phosphorus is a natural mineral that plants need for growth and metabolic functioning. For this reason, phosphate is often used as a fertilizer ingredient.

Information on whether phosphate is dangerous to human health is limited. However, what we do know is that phosphates can have a significant impact on our ecosystems, and can impact water quality – especially man-made inputs of phosphate, such as those in fertilizers.

It’s likely that you’d prefer not to drink phosphate in your water, especially as there is relatively little information about the health effects of this contaminant. In this guide, I’ve discussed how to tell if your water contains phosphate, how to test for it, and ultimately, how to filter it out.

โš›๏ธ How Does Phosphate Get Into Water?

There are several ways that phosphate can get into water.

This element can be found naturally in rocks, so it’s possible that phosphates may leach into natural water sources flowing through these rocks, such as streams and rivers. This water could eventually travel into reservoirs that are used for supplying public drinking water.

Phosphates are also found in decaying soils. When rain or snow seeps through these soils, it will pick up some phosphate. This water may then end up in underground well aquifers.

Phosphate is sometimes used as a fertilizer ingredient. If surface runoff occurs, and fertilizers end up in moving water, this water might then travel towards a well water or public water supply.

Phosphate as fertilizer

In some cases, phosphates are actually added to drinking water to prevent lead leaching from pipes. If your public water system consists of lead pipes, your local supplier might add phosphates to your water, which form a layer inside pipes and prevent lead from escaping.

๐Ÿ”Ž How Can You Tell if There is Phosphate in Your Water?

Phosphate has been reported to taste “sweet”, “bitter” and “metallic”, but in a relatively low concentration, you probably wouldn’t taste it at all.

Concentrated phosphorus also has a smell that is “match-like” or “garlic-like“, but again, you’re unlikely to notice this in your drinking water.

Phosphorus can be white, black or red, but in water, it is not usually visible.

In short, it’s unlikely that you will be able to taste, see or smell phosphate in your water. The only way to know whether your water contains phosphate is to test for it.

๐Ÿ”ฌ Should I Test My Water for Phosphate?

Whether you have a well or you get your water from a municipal supplier, I recommend testing your water for phosphate. This is because phosphate can get into well water naturally, or be added to your city water deliberately by your supplier. If you have city water your annual water report should list phosphate and the levels if they are present.

According to the Food and Drug Administration (FDA), inorganic phosphates are generally recognized as safe when used as food additives. They’re also considered safe to consume “at reasonable levels”.

However, phosphate is still considered a water contaminant, and there’s a lot that we don’t know about the long-term effects of consuming it in drinking water. You might simply want to remove phosphates from your water as a precaution – but you need to know that your water actually contains phosphate before you do that.

Whether you have reason to believe that your water contains phosphate (for instance, you know that your local authority adds phosphate to prevent lead leaching) or you’re simply curious, it’s worth paying for a phosphate test for a water sample in your home.

Water test

๐Ÿงช How to Test for Phosphate in Drinking Water

There are two ways that you can test for phosphorus: using a certified laboratory or buying an at-home phosphate test kit.

Certified Laboratory Testing

The best way to understand how phosphorus affects your water quality is to use a certified laboratory testing method.

My recommended certified lab is Tap Score by SimpleLab. The Essential Hydroponics Water Test tests for hydroponics nutrients, including phosphorus.

SimpleLab will send you a testing kit in the post. You can follow the kit’s instructions to take water samples, then post your samples back to SimpleLab for free. These samples will then be tested in a laboratory environment.

Your results should be emailed to you within 5 days. As well as telling you what your water contains, this method of testing also includes a health-risk assessment, treatment recommendations, and potential aesthetic and plumbing issues.

water testing with tap score

Water Test Kit

Phosphorus can create a harmful environment for home aquariums and fish tanks, as it alters the chemistry of water and can contribute to algae production, resulting in oxygen starvation.

This is likely unimportant to you – but it does mean that there are plenty of phosphorus test kits available online for fish keepers and home aquarium owners. These kits are used to test tap water samples to ensure they contain no phosphates before this water is introduced to aquariums.

You can, of course, use phosphate test kits for whatever purpose – and this method is also suitable for testing your drinking water quality. These kits are simple to use: just dip a strip into your tap water and wait for it to change color. Use the color chart in your kit to determine how much phosphorus your water contains.

This form of testing is less accurate, and won’t give an exact reading – more of a range. However, it can be a good option if you don’t know whether your water is contaminated with phosphorus at all, and you want to get a general idea before you pay for anything more expensive.

Phosphorus test

๐Ÿ“ What Can I Do If My Water Tests Positive for Phosphate?

If your water tests positive for phosphates, you can use one of several water treatment methods to remove this contaminant and improve your water chemistry.

Some of the best methods for removing phosphorus include the following:

Activated Carbon Filters

Activated carbon filters can remove a high concentration of phosphates. Charcoal carbon filters are especially effective, removing up to 70-90% phosphorus from drinking water.

You can buy activated carbon filters in a variety of applications, such as water pitcher filters, faucet filters and countertop filters. Carbon filters are also included in larger filtration systems, such as reverse osmosis filters and whole-house filters.

This method of filtration can also remove chlorine, heavy metals, pesticides and herbicides.

Because carbon filters are relatively cheap to make, they’re widely available in a range of applications, and affordable for most budgets.

You can buy a water filter pitcher containing an activated carbon filter for less than $20.

activated carbon filter cartridges

Reverse Osmosis Filters

Reverse osmosis filters offer a highly effective water treatment solution, removing a high concentration of phosphates, and up to 98% of all total dissolved solids.

This method of treatment sends water through several filtration stages and a semi-permeable membrane at a high pressure. The semi-permeable membrane contains tiny pores that only water particles can pass through. A range of impurities, including dissolved minerals, heavy metals, chemicals and microorganisms, are removed.

Reverse osmosis systems can be installed as countertop or under-sink applications. They can start as low as $ $250 and increase based on technology or contaminant rejection. You’ll also need to pay to replace the filters an average of every 6-12 months, and the membrane every 2 years, but best to follow manufacturer recommendation

Reverse osmosis (RO) filtration system


Distilled water is completely pure, containing only H20. A portable countertop distiller can reduce the concentration of phosphates by nearly 100%. Distillers can also remove a range of impurities, including heavy metals, chlorine, algae, bacteria, dissolved salts and minerals, and more.

A distiller boils water until it evaporates into steam. This steam travels through a cooling corridor, where it condenses into water droplets and drips into a clean container, as distilled water. The contaminants are left behind in the boiling chamber, and can be removed from the chamber when you clean it out.

Distillers are quite pricey initially, costing around $100-$300. However, this method of filtration is one of the most affordable to maintain in the long run, as you only need to pay to replace the tiny carbon filters at the distiller’s spout.

countertop water distiller

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