The main concern with drinking water supply systems is eliminating, or at least dramatically reducing, the spread of microbiological pathogens through the supplied water. This is generally known as water treatment, but it does not necessarily involve actually doing anything to the water. Other concerns with water supply systems have to do with the quality and usability of water, mostly relating to removing particulate contamination and/or chemical contamination.
Water Onboard Eva
Traditional Water Treatment
When we first got the boat the stainless steel tanks were coated on the inside with a fairly uniform soft layer of slimy material. This layer was about a sixty-fourth of an inch thick and pinkish gray in color. I assumed that this deposit in the tank was the result of many decades of use where city water was stored in the tank for long periods of time. To deal with this apparent problem I added several cups of 6% sodium hypochlorite solution to each 17 gallon tank, filled them to the top with city water and let it soak overnight. In the morning I drained and the tanks and rinsed them several times by filling them with water. At this point I considered the tanks sterile and safe for use, but this did not entirely remove the slimy build-up on the walls of the tanks. When I plumbed the boat I installed a charcoal canister filter after the foot pump for the galley sink, but I plumbed the hand pump for the sink in the head directly to the tanks. When we began using the boat I usually put a quarter ounce of 6% sodium hypochlorite solution in each tank when I filled them from empty. This made the water coming out of the head sink smell faintly like swimming pool water, but the water that came through the charcoal canister in the galley sink had no odor or taste of sodium hypochlorite.
When the charcoal canister was new the foot pump easily forced water through it and the system was very easy to use. The filter canister did not however remain clear and easy to pump for long. What was happening was that the slimy material that had previously been well stuck to the walls of the tanks was dying and falling to the bottom of the tank. Each time we would sail in rough conditions the accumulated gunk on the bottom of the tank would get stirred up and go into the filter. Since the filter cartridges were fairly expensive at nearly $20 a piece I kept trying to get the tanks clean enough that they would last more than a month. Several times I repeated the strong sodium hypochlorite solution overnight treatment, and I usually got quite a bit of dead pinkish gray tank wall slim out of the bottom of the tanks when I pulled the hoses off to drain them in the morning. Over time the amount of crud coming out of the tanks diminished, and within a year the filter cartridges were lasting six months each. We did however continue to have problems with the filter cartridges slowly plugging up so that pumping with the foot pump was quite a chore. Eventually after several years of struggling with the foot pump we decided to add an electric pump as well. At first I just added a small 1A 12V diaphragm type pump to the plumbing before the foot pump. This allowed us to continue to use the foot pump for carefully metering small amounts of water for normal washing and cooking while being able to more easily fill pots for boiling or containers for rinsing off after swimming in the salt water. This dual pump system worked quite well for several years, but the extra pressure was hard on the foot pump and it eventually failed. We replaced the foot pump with a spare and the system worked again for quite a while. When after about three years the pump failed we had to install our spare which was a bit higher capacity and it blew out the new foot pump very quickly. At this point I just removed the foot pump, and we had only the electric pump and a spare foot pump that could be installed in the event of electrical failure.
All around the world we just filled our tanks with any fresh water we could get, and I added the standard quarter ounce of 6% sodium hypochlorite to each tank. Sometimes when the water we got from marinas already smelled like swimming pool water coming out of the hose I dispensed with adding the extra sodium hypochlorite to extend the life of our charcoal canisters. Because of the small volumes of water that we put through the canisters though we never had any problems with them reaching their limit for the amount of sodium hypochlorite that they were capable of removing. We usually replaced the filter cartridges every six months, but sometimes they went nearly a year. To keep track of when to change the cartridge I always wrote the installation date on the side of new cartridges. The type of cartridges we used were not available in most of the world, so we carried a large stockpile that lasted us from Australia to the Caribbean.
When we filled the tanks with the reverse osmosis watermaker I never added sodium hypochlorite. There are two separate reasons why I considered the water from the watermaker to need no chlorination as long as our tanks remained sterile. One is that I considered that sea water in the open ocean contained no dangerous microbiological pathogens. The other is that the membrane that does not allow sodium chloride and other dissolved minerals to pass through most certainly does not allow something as large as a living organism to pass through. The water from the water maker was however somewhat unpleasant tasting simply by virtue of being devoid of all the dissolved minerals that we are used to in drinking water. The charcoal canister filtration of regular city water also caused this problem, but it was more pronounced with water from the water maker which then also typically went through the charcoal canister before it was used. To deal with this tasteless water problem we always tried to have a large supply of drink mix concentrates onboard. This was however somewhat problematic as some of the powdered drink mixes available around world were quite horrible. The worst problem was the drink mixes we got in Indonesia which contained some powerful diuretic, and were basically unusable. Universal availability of fresh limes, sugar and canned lime juice in Indonesia was however normally an acceptable substitute. Throughout SE Asia inexpensive packages of flavored noodle soup mixes were also available, which with fresh lime juice and bottled soy sauce were an enjoyable way to consume water.
Microbiological pathogens are living organisms that have a strong tendency to cause illness or distress when they take up residence inside the human body. From a water quality perspective this has normally been certain strains of fecal coliform bacteria that are particularly voracious multipliers in the digestive tract of humans and sometimes other animals. Just which bacteria are pathogens is a tricky distinction to make because just about any fecal coliform bacteria have the potential to cause discomfort or illness if the conditions are right. The reason for this is that the health problems associated with fecal coliform bacteria mostly center around someone's digestive tract being rapidly colonized, and if the living conditions are favorable even the rather benign fecal coliform bacteria can multiply rather quickly. Some of the more voracious strains of fecal coliform bacteria tend to cause illness in a significantly larger percentage of people who are expose to them, and these are the dangerous pathogens.
Somewhat conveniently those most voracious colonizers of digestive tracts also tend to not do well in water. This is where the traditional sentiments about the cleaner water looked, smelled and tasted the less likely it was to make someone sick. Cool, clear water may have some fecal coliform bacteria in it, but these strains of fecal coliform bacteria that survive well in water tend to be more easily kept in control in the digestive tract by natural mechanisms. Warm and dirty water with a large amount of organic material in it is more like the digestive tract of an animal, and is more likely to be able to support the dangerous pathogens. These are of course just general tendencies, and people have gotten sick enough from drinking cool clear water to make some form of testing or treatment standard practice.
There are other microbiological pathogens that may be found in water as well, but they are not usually the main focus of water quality programs. Names like crypto sporidium and geardia come to mind. In general fecal coliform bacteria are fairly easy to kill. Ultraviolet light usually gets them, boiling water usually gets them and they are large enough that they are also easy to filter out. Viruses on the other hand are smaller and harder to kill, because they are not technically even alive when they are being transmitted from one living organism to another. What does knock out all microbiological pathogens is chemical treatment of water with sodium hypochlorite. The reason that sodium hypochlorite is so effective at killing micro organisms is it's ability to break down most types of organic material. The hypochlorite ion with it's negative one oxidation state oxygen atom will react with most of the carbon containing organic molecules, breaking them down into smaller molecules.
The usual procedure for assuring a reasonable level of safety in water supplies is to use some means of filtration to remove sediment and any other material that causes water to have a pronounced color, odor or taste. Testing is then done to determine the amount of fecal coliform bacteria in the water, and if the level of fecal coliform bacteria exceeds some standard amount then calcium hypochlorite is added to the water. Calcium hypochlorite releases the same hypochlorite ions into the water, but is cheaper to handle than liquid sodium hypochlorite solutions.
The amount of sodium hypochlorite or calcium hypochlorite that is added to the water depends on how much organic material there is in the water. Since the hypochlorite ions react with just about all organic material any organic material in the water uses up the free hypochlorite ions. The amount of hypochlorite ion required to digest the organic material in the water is referred to the "chlorine load". If more calcium hypochlorite or sodium hypochlorite is added to the water it forms a weak solution of calcium hypochlorite or sodium hypochlorite, and the hypochlorite ion in this weak solution is referred to as "free chlorine". These traditional terms seem a bit misleading in their reference to chlorine, but hypochlorite ions and chlorine gas are closely related. If a solution of calcium hypochlorite or sodium hypochlorite is left exposed to the atmosphere the hypochlorite ions slowly disappear. As the hypochlorite ions disappear chlorine gas is released. If the calcium hypochlorite or sodium hypochlorite solution is stored in a sealed container the hypochlorite ions do not disappear nearly so rapidly because concentrated chlorine gas builds up in the air space above the solution. In the presence of chlorine gas hypochlorite ions are inhibited from breaking down to form chlorine gas. The reason that hypochlorite ions continue to slowly break down even in a sealed container is that the chlorine gas actually escapes through the container walls at some slow rate.
The trick that the Clorox corporation uses to keep hypochlorite ions in a plastic bottle for long periods of time is to add sodium hydroxide to raise the pH of the solution. A more acidic solution promotes the breakdown of hypochlorite ions, so driving the pH up makes sodium hypochlorite last a whole lot longer. This is an important piece of information for the use and storage of sodium hypochlorite solutions, but it also tends to scare people horribly. Oh no, sodium hydroxide, that is Red Devil lye, that stuff will dissolve the flesh right off of your fingers. Yes, of course sodium hydroxide is extremely caustic because it is a strong base. In an aqueous solution though sodium hydroxide does essentially nothing but raise the pH of that solution. In fact sodium hydroxide is by far the safest and least reactive means of raising the pH of a solution. The safest and least reactive means of lowering the pH of a solution is hydrochloric acid. If hydrochloric acid and sodium hydroxide are mixed together, a violent exothermic reaction takes place. Very spectacular and potentially dangerous. If the hydrochloric acid and sodium hydroxide are on the other hand mixed as aqueous solutions weak enough to temper the violent exothermic reaction then what you very unspectacularly get is just water with sodium chloride in it (salty water).
For large scale water treatment it is usual to leave just a small amount of "free chlorine" in the water so that it will be somewhat resistant to further microbiological contamination. To reliably get the stubborn viral microbiological pathogens a significantly stronger concentration of hypochlorite ions is required. If water is brought up to this higher hypochlorite ion concentration it is highly undesirable for use as drinking water, and it even becomes somewhat undesirable for bathing. There are however a number of ways to bring the hypochlorite ion concentration back down to safe and comfortable very low levels. One is just to let the water stand, but this can take months or even years if it is a large container of water. An activated charcoal filter will remove essentially all hypochlorite ion, and this is the normal way that small quantities of water are made palatable again after being heavily treated with sodium hypochlorite. Another way to bring the hypochlorite ion concentration down more quickly than just letting the water stand is to drive the pH down a bit. The best way to do this of course is by adding hydrochloric acid. The sodium hypochlorite and the hydrochloric acid react to form, yes you guessed it, sodium chloride (table salt). Since the quantity of sodium hypochlorite is very small the amount of sodium chloride produced is also very small, and the water does not become salty tasting in the slightest. The trick though is in what the final pH of the water is. The more hydrochloric acid is added, the more rapidly the hypochlorite ions will disipate, but the excess of hydrochloric acid drives the pH down. A slightly acidic water is no problem at all. Afterall the human body has quite a lot of hydrochloric acid in it naturally. If the pH is driven down so far that the water becomes even the slightest bit caustic though it is widely considered totally unsafe for drinking or even bathing in.
Filtration alone can also be used to control microbiological contamination of drinking water. This has been a widely frowned upon practice though because it requires very strict control procedures to work reliably. The main problem with filtration alone is that the dirty side of the filter element ends up just crawling with everything that is being removed from the water. A slight failure of the seal of the filter, or a plumbing or handling error when changing or cleaning filter elements can cause substantial contamination of what is supposed to be the clean side of the filter. The basic idea for filtration removal of microbiological contaminants is that the filter media has to be able to reliably remove the microbiological organisms, and the rest of the system has to be able to keep the dirt on the dirty side. The way this works is that filter elements have to either be disposed of or cleaned and sanitized periodically. When the element is to be changed the entire section of the plumbing on both sides of the filter has to be isolated with valves and then sterilized before normal operation can be resumed. Again sodium hypochlorite is the primary tool used for sanitizing the filter area, and much stronger concentrations can be used than are used for treating an entire water system. When done properly filtration can do a great job of removing microbiological contamination without any potential problems of unwanted chemical contamination of the water. This does however require filter elements fine enough to remove the smallest microbiological contaminants expected. Removing fecal coliform bacteria is fairly easy, but smaller viral spores can be problematic. In any case the filter media also removes darn near everything else from the water, and tends to plug up quickly making filtration a generally difficult and expensive endeavor for large scale water systems.
Where water comes from has a lot to do with how safe it is, and how it will respond to various types of treatment. Water that has a high quantity of organic material is both more likely to contain dangerous microbiological pathogens, and is also more problematic for hypochlorite ion based treatment. Not only does all that organic material require much larger quantities of calcium hypochlorite or sodium hypochlorite be added, but higher concentrations of the byproducts of breaking the organic material down can also be problematic. One particularly widely talked about byproduct of the action of hypochlorite ion is the formation of trihalomethanes. The basic idea is that when the class of compounds known as tannins are present in water the addition of calcium hypochlorite or sodium hypochlorite causes the formation of some compounds of the class trihalomethanes. What is not so often talked about is which tannins lead to the formation of which trihalomethanes, and even more importantly which of the trihalomethanes are the extremely toxic ones. In any case tannins are often present in surface water, and treatment with calcium hypochlorite or sodium hypochlorite can generate some small quantities of toxic materials. Tannins in surface water are primarily the result of tree leaves falling into the water and breaking down. As water flows down into larger rivers the concentration of tannins drops off dramatically. A convenient reality is that the upper areas of watersheds where tannins are found in higher concentrations typically are also the cleanest and least microbiologically contaminated water sources. Compounds from coniferous trees also tend to make for an acidic weak tea of needles that is not conducive to fecal coliform bacteria, so forest water sources very often are clean and ready to drink. Areas where large quantities of deciduous leaves drop into slow moving creeks in the fall can make some water sources heavily contaminated with tannins but also microbiologically unsafe. In these cases some additional treatment strategies are required.
Tannins can be removed by filtration, and this is the usual solution for large scale water systems. Another option is the filtration of the final product water where it is used. The trihalomethanes generally do not cause problems for irrigation, washing or even bathing, so the smaller quantity of water used for drinking can be filtered using an activated charcoal canister. The other option that is used surprisingly routinely is that a decision is made to simply not treat with calcium hypochlorite at all. Sometimes a water boil is issued when calcium hypochlorite treatment is deemed counterproductive in the presence of high concentrations of tannins, but this is usually an individual decision made by whoever is in charge of water treatment. An interesting tidbit of information is that most municipalities require that water treatment be overseen by a trained and certified expert, but they do not specifically require that the expert do anything to assure a safe supply of drinking water. If the guy in charge is particularly adverse to trihalomethanes (or some other byproduct of hypochlorite ion treatment) then what would normally be considered dangerous levels of fecal coliform bacteria may routinely be allowed to flow into the distribution system. As long as there is no outbreak of dysentery or cholera everything is considered hunky dory peachy keen.
Water that is drawn from deep wells generally is sterile, with nothing growing in it, but this does not mean that it is perfect for drinking either. The main concern for deep water is mineral contamination, and the most common problem is simply such a high concentration of certain calcium containing compounds that soap will not work. This is somewhat strangely known as "hardness", and is usually simply an annoyance that can sometimes be remedied with the use of a water softening additive. With high concentrations of minerals dissolved in deep well water there are possibilities of toxicity also, and it is usual for the water from a well to be analyzed for a large number of metallic and other contaminants to determine if it is safe for use as drinking water. In some places the deep water comes up almost as pure water with nothing in it, and in other places the water comes up so thick with minerals that it leaves fields white if it is used for irrigation. Again for drinking water it is the use of a charcoal canister filter that is best able to deal with the mineral contamination.
The other concern for surface water, and in some rare cases for deep well water also, is chemical contamination from human activity. Green, blue, purple, red and yellow water running out of a mining area not only looks bad for water quality, but can in some cases cause chemical contamination of creeks, rivers and lakes. Runoff from agricultural operations is notoriously dirty, and some pesticides, herbicides and agricultural growth hormones can build up in surface water systems. Runoff from paved roads is also notoriously dirty from lubricating oil and combustion byproducts. Especially in the first rain of the season creeks sometimes rainbow over from urban runoff.
Another significant concern is the simple mechanical disruption of soils caused by human activity. Cattle ranges become devoid of vegetation, torn up by hooves and can literally send a flood of mud into creeks, rivers and lakes. Exposed dirt in agricultural fields also sends mud, sediment and anything that washes out of the soil running into creeks, rivers and lakes. An even larger, but transient, sediment problem arises from large scale logging operations. The hillsides removed of their trees don't stay in place as well, and much more soil is carried into nearby creeks. Haphazardly created and heavily used dirt roads also tend to cause erosion and sedimentation problems.
What kind of problems for drinking water supply these human activities causes depends on the local situation. Obviously sediment getting into a water supply would universally be considered undesirable, but sediment filtration is both straightforward and extremely widely used. Larger concerns have to do with more toxic chemical contaminants that may also wash out of exposed soil. Generally the deeper the soil is disturbed the worse these chemical contamination problems are likely to be. Mining is notorious for contaminating creeks with things worse than the mud running off of cow pastures. Chemicals used in industry have also sometimes found their way into creeks, rivers and lakes, but this problem has been widely curtailed in recent decades. It has generally been easier for society to police toxins used in industry but not found in the local environment in large quantities. Toxins that naturally wash out of soil in small quantities are harder to police when they are caused to wash out in much larger quantities by human activity. Where is the line drawn, do we crack down on the kids jumping in mud puddles because they are artificially contributing to erosion, sedimentation of creeks and contamination of drinking water supplies? If the kids are allowed to have free rain with their rubber goulashes how then is someone removing logs from their property to be enticed to do it in a way that minimizes sedimentation of the local creek. Lots of work has been done on these issues, and the most successful strategy has actually been programs that offer education and incentives to small land owners to put effort (and often monetary investment) into keeping the land where it is. In the end most people are conscientious and moral, it is just a matter of making clear determinations about cause and effect and providing a support structure so that the good practices don't end up being financial suicide.
Other means of water treatment also exist, and have been used to various degrees of success over the course of human history. The oldest form of water purification was the use of ethanol producing yeast to brew beer. The basic idea here is that fecal coliform bacteria don't do well at all in a 5% ethanol solution. The origins of beer production come from a time when grain agriculture was creating large cities and high population densities. Under these population pressures heavily polluted rivers, creeks and lakes became spectacularly efficient mechanisms of transmission of voracious strains of fecal coliform bacteria. Just how beer production came about is a bit of a contentious subject, but it is probably an evolutionary adaptation. Beer production probably grew in popularity simply because people who drank nothing but beer were much less likely to become colonized by the most dangerous microbiological pathogens and were therefore stronger and better able to pass on their own genetic material.
A pint a day might be less of a health hazard than dysentery, but ethanol is in fact rather hard on the body and better means of assuring a safe drinking water supply have long been sought. In the 19th century the popular means of water purification was to drive the pH down so low that bacteria could not survive. This was done with carbonic acid, which was convenient in that it rapidly dissipated and left little or no residue in the water. And this is where soda pop came from. The basic idea for carbonic acid purification of water is to aerate the water with carbon dioxide for long enough that a solution of carbonic acid is formed. This considerably lowered pH solution is then left to stand in a sealed container for long enough that no bacteria remains growing in it. When the water is then to be used it requires further treatment of some kind to make it palatable. The carbonated water can just be left stand to dissipate on it's own, but this may take hours. Mixing the carbonated water with fruit juice or milk is one option. Diluting carbonated water raises the pH of the final solution, and reactive compounds in the fruit juice or milk also tend to accelerate the rate of dissipation of the carbonic acid as carbon dioxide. Then there is also the possibility of adding a base to neutralize the carbonic acid. This gets a bit tricky though because the water typically was not very clean in the first place, and the combination of pH values quite far from neutral with the energy input of a violent exothermic reaction tends to synthesize all sorts of unexpected compounds. Just what kind of a strange brew one ends up with after neutralizing the carbonic acid depends on what base is used and what was present in the water in the first place. Hence the murky art of the drug store soda jerk. I'll take mine with chocolate syrup and a scoop of plain vanilla ice cream thank you very much.