shower-head-water-quality-guide

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Shower head water quality matters for two different reasons. The first is mineral content. Hard water leaves deposits that build up on the face of a shower head and inside its spray holes, and the same minerals build up in water heaters. The second is microbial. A shower head is a place where water can sit between uses, and the water that leaves it is turned into a fine spray. This guide covers what a university extension source says about hardness, what two peer-reviewed studies found about Legionella bacteria in household showers, and where the public information stops. It does not recommend a filter, a water heater setting, or a cleaning product.

Quick answer

Hard water causes deposits. Penn State Extension states that hard water causes gray or white deposits when water is heated.
Scale can also build up on hot water heaters and shorten their useful life, according to the same extension source.
Legionella bacteria were found in household showers in both studies we opened. A 2019 Australian study found them in most of the 68 showers it sampled.
In the UK study, Legionella detected by culture was less common, at 8 percent of shower water samples. More frequent use and more frequent showerhead cleaning were associated with lower Legionella concentrations.
Neither source tests shower filters, so this guide cannot say whether a filter reduces hardness or bacteria in a shower.

How we chose

We limited this guide to three sources that could be opened and read in full or in a substantial abstract. The first is a Penn State Extension page on water hardness and softening, which is a university source for household water treatment. The second is a 2019 study published in the journal Pathogens and hosted on PubMed Central, written by researchers at Flinders University in Adelaide, Australia. The third is a 2017 study from the UK, published in the International Journal of Hygiene and Environmental Health, which is indexed on PubMed. The two studies are separate research groups in different countries, so we treat them as independent.

We did not use retail product pages, filter brand claims, forum posts, or blog summaries. None of the sources we opened tests a specific shower head or filter model, so no product is named in this guide. Where a number is not in these sources, we say so.

Hard water and what it leaves behind

Hardness describes the calcium and magnesium dissolved in water. Penn State Extension explains that the hardness level is reported as parts per million of calcium carbonate or as grains per gallon. The extension source gives a conversion, stating that a grain per gallon equals approximately 17 mg/l or ppm. That conversion is useful when you read a water test report, because the units may differ from one lab to another.

The extension source describes the visible effects. Hard water causes gray or white deposits when water is heated, and it leaves soap films and detergent curds in bathtubs. A shower head is a heated-water fixture, so deposits on its face and nozzles are one expected result. The source also says that scales can build up on hot water heaters and decrease their useful life. That is the same mineral process, just in a larger vessel.

The extension source treats hardness as a nuisance rather than a health problem. It states that water softening simply removes hardness minerals and eliminates problems that are a nuisance and not a threat to human health. It also says the decision to soften or not to soften is a matter of personal preference rather than necessity, and that the major disadvantage of softening is the potential health risk for people on low sodium diets. Those are the extension’s statements, and they are the reason this guide does not present softening as a health measure.

Where softening fits in a shower

The Penn State source gives a practical rule for which lines to treat. It says that showers, sinks, and laundry hookups probably should be softened, while toilets, outside spigots, and basement sinks can be bypassed. The source also notes that unless your water is extremely hard, not all incoming water needs to be softened. In some cases, the extension says, you may want to soften only the hot water.

The extension page explains the cost of softening in terms of sodium. It says that the exchange of hardness minerals for sodium adds 7.5 milligrams per quart for each grain per gallon of hardness removed. That is a number to weigh if someone in the house follows a low sodium diet. It is not a reason to skip a water test, because the extension source recommends having the water tested before choosing an approach.

Legionella in household showers

Legionella is a bacterium that can grow in water systems, and the two studies in this guide looked specifically at household showers. A shower can release water as a spray, and the researchers describe that spray as an aerosol. The UK study frames the question directly: household water systems have been proposed as a source of sporadic, community acquired Legionnaires’ disease, and showers are a frequently used aerosol generating device in the home. That framing is the study’s own, and the study does not say how often illness results from a given shower.

Both studies found the bacteria in household showers. The Adelaide study tested 68 showers. It reports that a total of 74.6 percent (50 of 68) of the showers were positive for Legionella species, and 64.2 percent (43 of 68) were positive for Legionella pneumophila. Those numbers come from a sample of homes in one city, so they describe that sample and not all showers everywhere.

The UK study tested 99 showers from 82 separate properties in the South of England. Using culture, it isolated clinically relevant Legionella species from 8 percent of shower water samples, representing 6 percent of households. A further 31 percent of showers were positive by Legionella species qPCR, which detects bacterial DNA rather than living bacteria. The study reports the two methods separately, so the two figures should be read separately.

What the studies say affects the level of bacteria

Neither study proves cause and effect, but both report associations that a homeowner can check against their own shower. The Adelaide study found that lower Legionella species concentrations were associated with higher hot water temperatures, with showers used at least every week, and with houses less than 5 years old. For Legionella pneumophila, the authors report no significant association with temperature, system type, or frequency of use.

The UK study reports that the concentration of Legionella species detected by qPCR decreased with increased frequency of use and with more frequent showerhead cleaning. It also reports that qPCR positivity was associated with the age of the property and the age of the shower. It found no association between qPCR positivity and the cold water supply or the showerhead material. Those are useful findings, but they are associations from one sample, not a guarantee that cleaning or a material choice will change the result in your home.

The Adelaide authors draw a practical conclusion from their data. They write that increasing hot water temperature and running showers every week to let water sitting in pipes be replenished by the municipal water supply were identified as strategies to reduce risk. That is the authors’ recommendation, not a finding that a particular setting is safe for a particular house. The sources do not give a recommended water heater setting, and this guide does not give one.

Water temperature and what the studies measured

The Adelaide study measured the hot water temperature at each shower and reports a range. It states that recorded hot water temperatures ranged from 34 to 68 °C, with a mean of 50 °C. The survey also showed a gap in awareness. 70% of participants did not know the temperature their hot water system was set at. That gap matters, because the study links temperature to the bacterial level.

The authors also cite a World Health Organization guideline that hot water systems should ideally maintain a temperature above 50 °C to reduce microbial colonization. We did not open the WHO source directly, so we report that guideline only as the Adelaide authors describe it.

What to do with this information

The sources point to a short list of steps a homeowner can check without special equipment. Start by knowing your water hardness. The Penn State source recommends having water tested, and it notes that a third-party lab test is not expensive. The test report will show hardness in one or both units, which lets you compare with the conversion in the extension source.

Next, look at how often the shower is used and whether the head is cleaned. The UK study associates more frequent use and more frequent showerhead cleaning with lower Legionella concentrations. Cleaning the face of the head to remove mineral deposits is consistent with that association, but the sources do not give a cleaning procedure or a product, so follow the head manufacturer’s instructions for your model.

Finally, if you are considering a change to the water heater or the hot water setting, talk with a licensed plumber first. The Adelaide study describes temperature as a factor in bacterial levels, but it does not give a safe setting for any house, and the sources here do not describe the scald risk of higher settings. A plumber can read the heater’s rating and the home’s layout.

What we could not verify

None of the three sources tests shower filters. We cannot say whether any filter, cartridge, or softener reduces hardness at the head, and we cannot say whether any filter reduces Legionella. Those claims are common in marketing, and this guide does not repeat them.

Neither study reports the hardness of the water it sampled, so we cannot connect their Legionella results to hardness. The UK abstract we opened does not mention hardness at all. The Penn State source explains hardness but does not measure any shower.

The two studies report different temperature summaries. The Adelaide study gives a mean of 50 °C in its results, and in another part of its discussion it describes the mean maximum temperature as below 50 °C. We report the range and the stated mean, and we do not resolve the difference.

The UK study reports that clinically relevant Legionella species were isolated from 8 percent of shower water samples. It does not connect that finding to any illness in the households it sampled, so we do not make a claim about illness rates.

The sources do not give a safe water heater temperature for any home, a cleaning method for any head, or a specific filter performance figure. The gaps are real. A reader who needs one of these answers should use a licensed plumber, the water utility, or the head manufacturer’s instructions.

Frequently asked questions

Does hard water damage a shower head?

The Penn State source says hard water causes gray or white deposits when water is heated. It describes these as deposits, and it does not describe damage to any particular head. Cleaning the deposits is the usual step, and the manufacturer’s instructions for your head apply.

Can a shower spread Legionella?

Both studies describe showers as aerosol generating devices and found Legionella in household showers. Neither study measured illness from a particular shower, so the sources support a finding about bacteria in showers, not a conclusion about illness risk for a given household.

Does cleaning the shower head reduce Legionella?

The UK study reports that more frequent showerhead cleaning was associated with lower qPCR concentrations. It is an association from one sample. It does not prove that cleaning removes the bacteria.

Should I soften all my water to protect my shower?

The Penn State source says showers, sinks, and laundry probably should be softened, and that not all incoming water needs treatment. It also notes the sodium trade-off and recommends a water test first. The decision depends on the test result and on household needs.

What hot water temperature is safe?

The sources do not give a safe setting for a particular house. The Adelaide authors cite a WHO guideline of above 50 °C to reduce microbial colonization, but they do not recommend a home setting, and this guide does not give one.