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Shower-head water filter tested

Some Hong Kong emigrants are concerned about a possible increased rate of hair-shaft breakage when washing hair in Britain's hard water (Cambridge nominally 322 CaCO3 + 122 Ca mg/L in 2017; HK averaged 56 mg/L in 1999/2000), and they say a shower-head water filter can help.

While I don't know enough about hair biochemistry or trichology to evaluate the claim that hard water increases the probability of breakage (or soft water reduces it), we can at least check if a shower-head water filter does indeed reduce the hardness. I was skeptical because I'd seen drinking-water filters operate at a much reduced flow rate, and while I knew reactions can speed up at higher temperatures, and a wider range of reactions are available if the water doesn't have to be rendered safe to drink, I still wanted to see some evidence that a filter mounted in a shower head really could work well enough at the higher flow-rate.

So we bought a "Shower Water Filter SWF1000" in 2017 from "UK Water Filters Ltd" (established 2003), for fitting to a "Mira Advance ATL 9.0" electric shower, and used "Palintest" water-hardness testing tablets (which turn soft water blue and hard water purple) to check it.

Baseline tests

To check that the testing tablets really would give useful results, we first of all tested water from the old shower-head (expected to be hard), and water from a "Brita" drinking-water filter jug (expected to be soft).

All test results were photographed so the colour values could be read out of the digital image (just in case my CVI impairs my judgment, although I'm normally not too bad with colour). To avoid issues with CRI we used daylight for the digital photography, but we couldn't keep its intensity constant so we included a white plastic background for calibration. We let the test bag dry for 48 hours between these tests.

The hard warm water from the old shower-head turned purple very quickly: the camera registered RGB colour values ranging from 784f6f to 836a7c against a background ranging from a1aba2 to 9aa49b. So far so good.

The filter water was more surprising---it was initially quite purple (6e6582 to 7a6c85 with a few parts as deep as 67447c, against a background of 96978f to acacaa) but when about half was poured away the rest was bluer (727995 to 898d99 with some parts 59657d and even 45536d). We suspected that water droplets left over from the first test, after they evaporated, might have left enough residue in the transparent plastic bag to turn nearby quantities of the filtered water purple. (This water was at room temperature, so the reaction took a little longer. We would have liked to keep the temperature constant for all tests, but the shower had no documented way of turning off its heater and we had no way of heating filtered water without bringing it into contact with other potentially-contaminating surfaces. We later found the ATL 9.0 shower does have an unheated option if the dial is turned anticlockwise past its setting "1", but the only mention of this in the manual is an unclear reference to "full cold" in the setup instructions.)

A second test with the 'Brita' filter was more clear-cut. This time we filled the test bag directly from the dripping water coming out of the filter cartridge---we didn't let it first come into contact with the jug, in case our jug had somehow become dirty enough to re-contaminate it---and we twice washed out the test bag with water under test before conducting the test. The result was a fairly uniform blue: 306479 to 50767f against a background of 91998e to acb0a1.

So yes our "Palintest" tablets were working correctly---they were not unconditionally turning purple. (And yes the "Brita" filter was working, or at least its central part was.) But if re-using a test bag you had to be careful to wash it thoroughly with water under test before running the test.

SWF1000 test

To ensure the test was conducted as fairly as possible without prior residue in the bag, we used a brand-new test bag and also washed it out with water under test before conducting the test. I was also careful to hold the bag in such a way that the shower water did not touch my fingers before entering the bag.

The resulting water was consistently in the purple (hard) range: 77496d to 785870 against a background of a9b0a8 to 979c95. The reaction was quick, and there were negligible differences when the test was repeated after the shower had been running for 10 minutes, and negligible differences whether the shower was set at its coldest setting (unheated), set at its hottest setting, or set mid-way in between.

The SWF1000 also had a green band of plastic printed with numbers up to 12, but (as can be shown by opening it to reveal the filter cartridge) this is not a settings dial. It seems the designers meant you to position it so as to remind you in which month of the year the filter was last, or should next be, changed (the marker symbol was like a clock inside a circular 'renew' arrow). This wasn't mentioned on the printed sheet of instructions that came in the box, probably because UK Water Filters said they'll send you reminders.

We tried removing the cartridge, holding it under a slow-running cold tap, and ensuring to capture only water that went through the cartridge without contamination from water that went around the cartridge, to see if the problem was with the cartridge itself or if it was due to the water having found some way to leak around the cartridge within the shower-head. But in this cartridge-only test, we still got the same range of purple (hard water).

So does it work at all?

UK Water Filters were kind enough to send us a response:
This filter will not reduce the hardness reading.

Only a salt based softener will reduce hardness readings because only a salt based product removes the calcium.

The [SWF1000] filter contains ceramic beads with will oxygenate the water making it feel softer, but it will not remove the calcium from the water.

We can confirm the water from the SWF1000 does indeed appear more aerated if collected in a glass, but I can't help wondering if this "filter" really is the best way to build an aerator. After I asked if any shower-head filter will actually soften the water they said:
Unfortunately, I am not sure there is a shower head on the market that will actually soften the water by removing the calcium. The only thing to remove the calcium completly would be salt which would requite a salt softening system to be plumbed in.
which is not an option for most tenants.

So the question remains: why has it been said that some Hong Kong emigrants feel "shower-head filters" counterbalance the effect of Britain's hard water on their hair, if those devices do not actually soften the water?


When we were asking about returning the shower head, another employee wrote:
The shower filters are great for removing chlorine which is good for hair and is the main cause of skin irritations. You would need a proper softener if you need the silky soft feel of water.
But Hong Kong's chlorine level is about twice that of Cambridge. (Cambridge average chlorine concentration in 2016, measurements taken at an area near us, was 0.34 mg/L free chlorine and 0.42 mg/L total, with no chloramine; Hong Kong's 1999-2000 level averaged 0.7 mg/L free chlorine. In both cases residual chlorine keeps pipes clean.) Swimming-pool chlorine levels are supposed to be 1--3 mg/L (i.e. 3--9 times Cambridge's tap-water level or 1½--4 times HK's) and there are concerns that frequent swimming can replace the natural sebum and leave the hair more brittle, but it's difficult to find hard data on how much of a problem this is at the lower chlorine levels of tap water. If a shower-head's removal of chlorine would explain the reported experience of the Hong Kong emigrants, then we're looking at a hypothesis along the lines of "the reduction in damage from chlorine removal, counterbalances (the increase in damage from water hardness, less the reduction in damage from there being lower chlorine levels to start with)". This is hard to test.

But the rate at which free chlorine escapes from water by off-gassing should increase with temperature and motion, so I'd expect any hot shower to deliver a higher percentage of its chlorine as a gas rather than leaving it dissolved in the water. (Some people are more concerned about inhaling chlorine than they are about chlorinated water coming into contact with their hair, and in that case you'd have to check how much of any chlorine removed from the water still ends up in the air---the filter is rather close, and it's not easy for it to just "hold on" to a gas. Good ventilation is probably the answer to that one.)

We have not been able to perform OTO/DPD tests to properly verify a comparison of chlorine levels in shower water.

Flow-rate and aeration

One thing the SWF1000 obviously does do is reduce the water flow rate---and it's possible that this might affect the rate of hair-shaft breakage during showering. The writers of US patent 6264121 B1 in 1997 seemed to think so, saying people who have their hair treated with "straighteners, permanents, conditioners, coloring agents, bleaches, and so forth" will find that "rinsing is preferably accomplished with a gentle spray to avoid doing additional damage to the hair", although given their track-record with software patents I'm not sure if we should consider a paragraph to have been properly peer-reviewed just because it's been accepted by the United States Patent and Trademark Office.

If some HK emigrants in the Cambridge area have seen an apparent reduction in the amount of hair trapped in their shower drains after fitting a shower-head filter, then it's plausible that their observations could be explained simply from their reduced flow rate.

In constant-heat electric showers, where the resulting temperature is determined entirely by the overall flow rate through the system, I'd expect a reduced flow rate to result in increased temperature regardless of whether this is effected on the shower controls or by a flow-reducing shower head, but if the shower-head is also aerating (adding air to) the water, this might offset the temperature increase.

Aerated shower heads reportedly collect more bacteria, which is probably why this one requires its cartridge to be changed every 6 months (at an annual cost exceeding that of the head).

Another way to have reduced flow rate without excessive temperature when the heating element cannot be changed, especially for shorter people, is to raise the head higher on its rail---the water should cool a little during its drop.

Reviews and returns

The supplier's web site showed a number of 'five-star' and 'four-star' customer reviews, and a mechanism to submit new reviews. But they do not promise that all submitted reviews will be published. I submitted a three-star review and so far it has not been published. Therefore we don't know the actual proportion of customers (or of the subset of customers who bother to write reviews) who felt they had a 'five-star' or 'four-star' experience---we just know that some did (assuming the published reviews are genuine).

However, we can confirm that their 90-day returns policy did work as advertised---they gave us a Freepost address to put on the box, we dispatched it 3 weeks after purchase and were refunded 2 weeks later. (The only minor 'glitch' was that the refund went to the Paypal balance, not the bank balance; Paypal's notification of this was taken out by a 'spam' filter, so we didn't know we'd got it until an additional 2 weeks had passed and we started making enquiries.)

All material © Silas S. Brown unless otherwise stated.