https://www.ncbi.nlm.nih.gov/pubmed/30326398
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4050989
https://www.ncbi.nlm.nih.gov/pubmed/26313703
https://www.ncbi.nlm.nih.gov/pubmed/20183522

To filter tap water, you can buy tea bags and fill them with a mix of the following:
1) activated carbon
2) “nuclear grade” mixed bed DI resin (aka ion exchange resin)

The activated carbon will help remove many toxins, including chlorine, chloramine, and endocrine disrupters, such as BPA and other pthalates, that leach from plastics. 1 2 3 4
The resin will remove chlorine, chloramine, and any other ionic minerals. Just to be sure, you can replenish the beneficial minerals with a daily multivitamin, or just eating some food can work wonders. The resin will also remove flouride, but weakly due to flouride being a low-selectivity anion.

Dow states: “Fluoride is a very low-selectivity anion so it cannot be removed from water without first removing all of the higher-selectivity anions like chloride or sulfate. Anions are removed according to their selectivity as described in the table of selectivity data. Fluoride can be selectively removed with activated alumina. There are many suppliers available for this media.” However, activated carbon will help protect the ion exchange resin from chlorine: “Used in combination with activated carbon for the added ability to remove of organic chemicals and parasites and to protect the resin from chlorine.” Source Reducing the PH by way of adding ascorbic acid (Vitamin C) to the water helps in removal of chloramines +1 and fluoride, by way of carbon and exchange resin, respectively.

Should I be adding activated alumina? Will activated alumina interact with the carbon or the resin, or add anything back to the water?

Brian from custompure.com answered:
“I’m assuming you are looking for something portable, as you are using now, to remove fluoride. I have good news for you: Mixed bed resin will remove fluoride. Activated alumina, also, will only work within a specific pH range, and is less effective than the mixed bed ion exchange resin. Link: http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2006.394/pdf
Out of curiosity, how do you know when to change the ion exchange resin? Are you using a TDS meter?
If you are looking for something to remove contaminants for water in your household, we do offer systems similar to (but smaller than) the ones we have installed in stores like PCC.”

Brian also added:
“I have another note about fluoride regarding selectivity: Stronger bond (high selectivity) ions will kick off weaker bond ions. What this means is that, at first, your resin is a free for all, grabbing everything it can. Then, when all of the binding sites are taken up, the high selectivity stuff will start kicking of the low selectivity stuff. So as you continue to introduce more contaminants (by adding new water when you refill your container), more and more low selectivity ions will be kicked off and replaced by the high ones. This is partially why I asked about a TDS meter- by the time you can taste a difference, you’ve already kicked off virtually all of the fluoride ions (fluoride doesn’t have a flavor or a smell).”

Sodium hydroxide is added to NYC water to increase the PH to 7.3. Sodium hydroxide is also used to flush out and renew ion exchange resin: “For anion resins, regeneration typically involves treatment of the resin with a strongly basic solution, e.g. aqueous sodium hydroxide. During regeneration, the regenerant chemical is passed through the resin, and trapped negative ions are flushed out, renewing the resin exchange capacity” Source. Adding ascorbic acid (the actual Vitamin C) to sodium hydroxide produces sodium ascorbate (C6H8O6 + NaOH → C6H7NaO6 + H20). Sodium ascorbate is the most bio-available form of vitamin C (it is approved for use as a food additive in the EU, USA, Australia and New Zealand), although it could exert pro-oxidative effects on DNA. I assume the amounts involved will be miniscule. PH of 7.3 is hardly a basic solution, so I will skip this step unless the filtering isn't what I expect (after I get a TDS meter).

What happens to chloramines in an ion exchange system?
“Chloramines are formed by the addition of chlorine to ammonia according to the following equilibrium equations:
Cl2 + H2O « HOCl + H+ + Cl-
HOCl + NH3 « NH2Cl + H2O
HOCl + NH2Cl « NHCl2 + H2O
HOCl + NHCl2 « NCl3 + H2O
Since these reactions are in equilibrium, it is possible that free chlorine will be present under certain conditions of pH, temperature and the ratio of chlorine to nitrogen. Free chlorine will degrade an ion exchange resin. This occurs primarily via decrosslinking in a cation resin and defunctionalization in an anion resin. In addition to the free chlorine that is formed when the equilibrium is shifted on these equations, the chloramines, while less oxidative than chlorine, will oxidize the anion resin functional group. Chloramines and free chlorine should be removed prior to ion exchange resin beds. Degradation products of these reactions include ammonia, hydrochloric acid, nitrogen, and in the case of anion resin oxidation - trimethylamine. The ionic species will likely be removed from the water by the downstream ion exchange resin and seldom have an impact on product water quality.” Source

“If water is held in the carbon block for longer period, microorganisms can grow inside which results in fouling and contamination. Silver nanoparticles are excellent anti-bacterial material and they can decompose toxic halo-organic compounds such as pesticides into non-toxic organic products.” Source

The carbon tea bag can be reused up to 50 times, although I'm not sure how many times the ion exchange resin can be reused. I will be trying out a TDS meter. Ok, a long time has passed and I finally got around to getting results from a couple TDS meters:

stanley stainless steel bottle
43 ppm tap
32 ppm after 8 hrs

annie's place with terrible tasting water
34 ppm after 8 hrs
31 ppm after new filter + 5 hrs

39 ppm tap
38 ppm after 2 hrs
36 ppm after 6 hrs
18 ppm after 12 hrs, very low volume remaining in bottle

gaiam stainless steel bottle
32 ppm after 12 hrs
41 ppm tap

glass bottle
29 or 33 ppm after 1 day depending on which tds meter
22 or 25 ppm next day half volume

It seems the tea bags are a somewhat effective, but require a long time to filter the water. I will next try taking a bottle with me, so that it gets juggled around. Maybe the agitation will speed up the filtering process. However, the numbers above, even at 18ppm, is rather poor based on the numbers I remember reading about in a forum, where the forum was about more sophisticated filters including reverse osmosis. My source for carbon is “Marineland black diamond media premium activated carbon”. My source for ion exchange resin is “Puroflo Mixed Bed DI Nuclear Grade” part number WS-MBDI-NG.

After taking a bottle with me cycling, the ppm on both tds meters was 3!!! That means that shaking the water up moved the molecules around sufficiently so that they eventually made contact with the media. Also, the media had already been used in my water bottle for two weeks (although I had a larger glass bottle with a teabag filter, that I used as a first stage, pouring water from it to my drinking bottle). The results are therefore comparable with a reverse osmosis filter.

My original thought was that water molecules in an unshaken container were always moving around much like in a gas, but at much closer range. This does not appear to be so much the case. What gave me this idea, is that food coloring dropped into water disperses rather quickly. However, this is a different phenomena. I believe dispersion happens because of the Van-der-waals forces between the food coloring and the water. The higher energy state and the ensuing need for entropy disperses the food coloring evenly among the water molecules. Therefore, it appears that in order to speed up the process of getting the non-water molecules over to the tea bag (to get attached to the media), some shaking is required.

My solution was to get a small 3 watt submersible fish-tank pump for $3 on ebay, which I put into a gallon glass jar (the kind used for pickles) along with the tea bag. I measure the PPM after the water filters overnight. Now I can tell when the filter material is used up, because the lowest PPM attainable quickly increases. The lowest attainable has shown anywhere from 0 to 2 ppm. When it gives up the ghost, the lowest quickly increases to 7-15ppm. I think this happens after about 10 gallons / 40 liters, but I haven't been keeping track.

In hoping to have the filtration take less time, and possibly use the media more uniformly, I've wanted to try putting the pump in line with a refillable filter cartridge, such that the water is forced through the media. However, I can't seem to find one that is less than the standard 10 inch length, and that will not fit well in a glass jar. It would have to be a very big glass jar and I'm not sure where to find such a beast.

On ebay I saw some very small funnels for a dollar, that I hope will fit on the intake of the water pump. The idea is that the tea bag will get stuck in the funnel and the water will be forced through it. So far, I've been having the tea bag circle along in the current created by the pump, by placing the pump at a higher level than the tea bag. The tea bag floats around close to the bottom. Without the funnel, if the tea bag gets caught on the intake of the pump, the small surface area of the intake, covered by the tea bag paper, does not allow a sufficient amount of flow.

What Does a TDS Meter Not Measure? source

“ Because TDS is an aggregate measure of charged compounds in water, uncharged things like motor oil, gasoline, many pharmaceuticals, and pesticides do not contribute to a TDS measurement. For example, the glass on the left in this article's header image contains deionized water with Malathion (an organophosphate pesticide) dissolved into it at 100 times higher concentration than allowed by the EPA for drinking water, and the TDS probe reads 000. “
I thought the whole point of anything being able to dissolve in water, was that it needed to be ionic: that's why oil and water don't mix? Well, I'm wrong. From wikipedia:
” Dissolved organic solids, such as sugar, and microscopic solid particles, such as colloids, do not significantly affect the conductivity of a solution, and are not taken into account. ”

Again, one of the other reasons I'm using activated carbon is to help remove plastics. Yet when I put a tea bag of carbon in my camelback, the water still tastes like plastic. I need to try and see if the tube or bladder causes the most effects. In any case, it appears that the plastic overwhelms the tea bag. They have inline carbon filters for the hose line, that may help, but I'm going to accept some plastic on my hikes for now. The carbon does keep the plastic taste from forming in my cycling water bottle, however.

Update: I spent a week in Somersworth, NH, and the tap water quality is horrible, in terms of a TDS reading of 150ppm, compared with nyc 40ppm. A single tea bag filter (working with the pump) was only good for purifying 6 liters of water to 1ppm. After that, the next 6 liters went no lower than 82ppm. I continued filtration with an unused filter.

Update: If you want to remove flouride, a TDS meter will not be that helpful, because flouride is added to water at 1ppm. The TDS meter does not have enough resolution to estimate the percentage of flouride that is removed by your filter.

“ The problem with the Zero unit, you see, is that pure water seeks to become contaminated. It will hungrily absorb CO2 from the atmosphere, forming carbonic acid, as well as any contaminants in the air. More dangerous is the fact that the Zero Water Filter removes 100% of the chlorine form the water. If your municipality did that, your community would suffer another yellow fever, legionella or other bacterial/viral disease outbreak.

Bacteria will grow in water that has no chlorine in it. If you use the Zero Water Filter remember that the filtered water is chlorine free. Also remember, ion-exchange resin is also a great medium for growing bacteria. The TDS meter on this device measures electrical resistivity or conductivity. It has no capacity to measure algae, fungi and microorganisms in your water.

The purification technology in this unit itself is sound, but the product has no technology to keep the water pure once it is made so. In water treatment science it is more expensive to keep water pure than it is to make it pure. I am willing to bet that if you do not sterilize your pitcher daily, you have bacteria growing in the system. ” source

In order to reduce the bacterial load on a filter cartridge, it's best to have a large family that will use up its filtering capacity quickly (so that the water filter gets replaced frequently).

Comparing the “zero water filter” with the “ion-exchange + carbon tea bag” (see section “method” above):
Since you will more often discard a tea bag than a larger filter cartridge, maintaining sanitation of the filter media is easier with tea bags. A glass jar is also easier to maintain sanitary, compared to a plastic carafe. The only weakness in filtering with a tea bag is the need for a small water pump.

Pure water will strongly attract any impurity, including contaminants in the air. In order to keep purified water pure, after being transferred out of the filter, you should continue to keep it in a glass container with a sealed lid. Another option is to dirty the water so it is no longer pure! Add some lemon juice, tea, cinnamon sticks or cloves.

It's not advisable to boil pure water, because it will become contaminated quickly. If you must, you can use a stainless steel tea kettle to boil the water, as stainless steel is highly unreactive.

Demineralized water has been claimed to have negative health effects because of a reduction in beneficial minerals.

http://jwh.iwaponline.com/content/6/4/433
A systematic review of analytical observational studies investigating the association between cardiovascular disease and drinking water hardness (2008)
“This study found significant evidence of an inverse association between magnesium levels in drinking water and cardiovascular mortality following a meta-analysis of case control studies. Evidence for calcium remains unclear.”

http://journals.sagepub.com/doi/abs/10.1097/01.hjr.0000214608.99113.5c
Review of epidemiological studies on drinking water hardness and cardiovascular diseases (2006)
“Many but not all ecological studies found an inverse (i.e., protective) association between cardiovascular disease mortality and water hardness, calcium, or magnesium levels; but results are not consistent.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854772/
Relationship between Tap Water Hardness, Magnesium, and Calcium Concentration and Mortality due to Ischemic Heart Disease or Stroke in the Netherlands (2009)
“We found no evidence for an overall significant association between tap water hardness, magnesium or calcium concentrations, and IHD mortality or stroke mortality. More research is needed to investigate the effect of tap water magnesium on IHD mortality or stroke mortality in subjects with low dietary magnesium intake.”

http://journals.lww.com/epidem/Abstract/2000/07000/Magnesium_in_Drinking_Water_in_Relation_to.9.aspx
Magnesium in Drinking Water in Relation to Morbidity and Mortality from Acute Myocardial Infarction (2000)
“The odds ratio for death from acute myocardial infarction in relation to water magnesium was 0.64 (95% confidence interval = 0.42–0.97) for the highest quartile relative to the three lower ones.”

https://examine.com/supplements/magnesium “Magnesium deficiencies are common in the western diet because grains are poor sources of magnesium.” People must not be eating much of the following: https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Minerals/Food-Sources-of-Magnesium.aspx

“Epidemiological research in the US, Europe, and Russia suggests health benefits may be associated with at least 20-30 mg/l calcium and 10 mg/l magnesium in drinking water.” Which on average agrees with what is supplied municipally. Source

“Recommendations for magnesium have been put at a minimum of 10 mg/L with 20–30 mg/L optimum; for calcium a 20 mg/L minimum and a 40–80 mg/L optimum, and a total water hardness (adding magnesium and calcium) of 2–4 mmol/L” Source: František Kožíšek, M.D., Ph.D via Wikipedia. Following this recommendation, even if the other elements are not counted, the sum of 25 mg/L of magnesium plus 60mg/L of calcium would have us drinking water that is 2.5 mmol/L. Using 30mg and 80mg, respectively, gives 3.2 mmol/L. Hardness is usually measured by CaCO3 (calcium carbonate). Source 2 mmol/L = 200.17 mg/L of calcium carbonate, which, according to the following table, is very hard water.

Concentration as CaCO3 Indication
0 to 60 mg/L Soft water
60 to 120 mg/L Moderately hard water
120 to 180 mg/L Hard water
180 mg/L and above Very hard water

Following the recommendation would lead to very very hard water, considering that elements besides calcium and magnesium are not included. It's probably safer to just have what's natural. So what is natural? “The hardness of local water supplies depends on the source of water. Water in streams flowing over volcanic (igneous) rocks will be soft, while water from boreholes drilled into porous rock is normally very hard.” Source Also, the mineral content varies greatly depending on the source, where, for example, even if the water is hard, magnesium may not be a part of the water supply (unless added by municipalities).

The recommended daily intake for magnesium is 400mg. A liter of drinking water in the U.S. has about 10mg/L of magnesium. It's recommended to drink 2 liters a day. That's 20mg of Magnesium from drinking water. Um… that's significant? There was a study that showed people drinking demineralized water urinated 20% more. Maybe they liked the water better? I guess I'm going to keep taking my multivitamin and magnesium supplement, and I hope I'll be ok. That along with my raw milk

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491930

 Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis (2012)

 Although reports from the World Health Organization and national agencies have
 generally focused on beneficial effects of fluoride (Centers for Disease Control
 and Prevention 1999; Petersen and Lennon 2004), the NRC report examined the potential
 adverse effects of fluoride at 2–4 mg/L in drinking water and not the benefits or
 potential risks that may occur when fluoride is added to public water supplies at
 lower concentrations (0.7–1.2 mg/L) (NRC 2006)

I'm not willing to stake that fluoride is good at 1 mg/L, and bad at 2mg/L. The ion itself is not used in any natural process by the human body. It is not a nutrient. There is no US RDA. It simply acts as a toxin, at any concentration, and the effects are noticeable when there is enough of it. In the following paper, when it says “no evidence exists”, it means that there hasn't been any scientific research done, not that it has been proven to not be harmful.

http://www.rph.org.nz/content/be2be2c4-4fef-49cf-93d6-172f2c8e4a88.cmr

 Review of Scientific Papers Relating to Water Fluoridation
 
 Beneficial effects
 
 a) Dental caries
 • Water fluoridation reduces the prevalence of caries in both children and adults
 in populations receiving water containing fluoride. Estimates of the mean
 difference in the proportion (%) of caries-free children place the figure between
 14–15% [11, 13]. An estimate of the prevented fraction in adults was 27% [6].
 6, 7, 9, 11, 13, 17,
 21, 22
 • Water fluoridation has a beneficial effect (on caries) over and above the effect
 of fluoride from sources other than water.
 11
 • While water fluoridation reduces caries, topical application of fluoride is a more
 efficient way of achieving protection (i.e., post-eruptive action – although the
 relative contributions of pre- and post-eruption are argued).
 15, 21, 22
 • Differences in caries rates between fluoridated and non-fluoridated
 communities are smaller than has been found previously. The increased use of
 other sources of fluoride, such as fluoridated toothpaste, appears to be the
 reason.
 15, 18
 • Communities receiving fluoridated water have consistently lower rates of caries
 than those receiving non-fluoridated water.
 6, 15
 • Cessation of fluoridation can result in an increase in caries. 9, 12
 • There is limited knowledge of the efficacy of fluoride in reducing caries if the
 fluoride concentration in water is reduced below levels presently considered as
 optimum.
 15
 b) Redressing social inequalities
 • The evidence for water fluoridation reducing differences, due to socioeconomic
 status, in oral health is inconclusive.
 3, 11, 17, 21, 22
    
 Adverse effects
 
 a) Dental fluorosis
 • Dental fluorosis is a demonstrated and acknowledged adverse effect that can
 arise from fluoridation.9, 11, 13, 22, 24, NFIS 35
 • There is a dose-response relationship between fluoride concentration and the
 prevalence of fluorosis, but the fluoride concentration threshold at which
 fluorosis becomes evident has not been determined. The prevalence of
 fluorosis at a drinking-water fluoride concentration of 1 mg/L was estimated to
 be 48% [11].
 11, 22
 • Fluorosis arising in areas with fluoride concentrations close to optimal (ca.
 1 mg/L) is usually described as very mild or mild.
 13, 24
 • In some communities (reported in the European Union and United States) an
 increase in very mild and mild fluorosis has been reported in communities
 receiving fluoridated water.
 24
 • The most likely contributor to the increased prevalence of fluorosis, where
 reported, is increased use of fluoridated products (particularly adult-strength
 toothpaste) by children under six years of age.
 2, 15
 • Sources of fluoride other than fluoridated water, such as fluoridated
 toothpaste and fluoride tablets, are risk factors for the development of
 fluorosis.
 24
 • The association between fluorosis and use of infant formula increases with the
 level of fluoride in the water supply, but the evidence for this being due to
 fluoride in the formula is weak.
 8
 • The total fluoride intake, not just intake from water, of an individual is the true
 determinant of the risk of fluorosis, and it is important that contributions from
 all sources are determined.
 7, 10
 • The most critical period for exposure to fluoride with respect to the
 development of fluorosis of the upper anterior incisors (those of greatest
 cosmetic importance) is the period between the ages of 15 and 30 months.
 2, 10
 • Recent overseas studies have consistently shown that very mild fluorosis does
 not have an adverse effect on oral health-related quality of life, but severe
 fluorosis is consistently reported to do so.
 4
 b) Other adverse effects
 • There is no evidence showing that water fluoridation increases the likelihood of
 hip fractures in the population receiving the water.
 2, 7, 11
 • Water fluoridation appears to have no effect on the likelihood of bone fracture,
 reduced BMD, or reduced bone strength, and some evidence suggests that
 fluoride concentrations around 1 mg/L may be beneficial. (NB. Reviews 7, 9
 and 11 concluded that there was insufficient evidence to assess the effects of
 fluoridation on bone disorders other than hip-fractures).
 5, 13
 • There is either insufficient evidence to assess the effect of fluoridation on other
 adverse effects, or the available evidence indicates there is no influence.
 7, 11, 13, 14, 22,
 25
 NFIS 36
 c) Effects from fluoridation chemicals
 • There is no evidence that, following the dissolution of fluoridation chemicals
 during the fluoridation process, any adverse effects will arise from the
 undissociated chemicals themselves, fluorosilicate species, impurities in the
 chemicals, or the dissolution of metals in water systems because of a
 substantial depression in the pH of the water.
 

Should drinking water be at a certain pH? Well, I'm taking the pH out and making it completely neutral with the ion exchange resins. There is some marketing fad to sell alkaline water. If it's supposed to be basic, then I've got that covered because I brush my teeth with baking soda. The food you eat will have so much more ions in it than the trace amounts in water. Does it matter that it goes in with the wrong pH, if it quickly gets mixed up with the food in your belly?

Related article: Alkaline Water: Benefits and Risks, healthline.com 20190530