Pure water is a molecule containing two atoms of hydrogen and one atom of oxygen. Another way of looking at it is to consider the water molecule as a compound of one hydrogen ion (which has a positive charge) and one negatively charged hydroxyl ion, which in itself is one hydrogen atom bonded with one oxygen atom. This is vitally important because cellulose is also made up mainly of hydrogen and hydroxyl groups bonded together with carbon and oxygen. The free hydrogen and hydroxyl ions attract each other. The cellulose molecules have hydrogen and hydroxyl ions which attract those in the water and in other cellulose molecules. When a sheet of paper is first formed, the millions of fibers, dispersed freely in the water, now come into contact as the water drains away. The vat is likely to contain 99 percent water, and the newly formed sheet will not be much less after couching. With strong hydraulic pressing, the water content will be reduced to about 50 percent. As the paper dries, capillary action initially draws the fibers and their molecules increasingly close together. The hydroxyl and hydrogen ions in the molecules come closer to each other, until there is growing competition for the remaining free ions in the water. When I was at university I often had debates with a textile technology friend who maintained paper could never be strong enough to make clothes as it was only held together by "hydrogen bonding." My response was to point out that textiles were only held together by friction! The negatively charged hydroxyl ions can dissociate further into negatively charged oxygen ions and more positively charged hydrogen ions. Water thus contains large amounts of free ions—of opposing charges—and these are attracted to the ions in nearly every other element to the extent of breaking apart other types of molecules. It is this unique property that enables water to dissolve more substances than any other liquid, which earns it the soubriquet "the universal solvent." Water can also dissolve or suspend a huge variety of additives like size, pigments, dyes, and fillers. Historically, papermakers obtained their water from rivers and springs. In either case, the ultimate source is rainwater. Although we might think of rainwater as pure, it will at the very least contain dissolved carbon dioxide and—if the air is polluted—it may contain sulfate, nitrate, or chloride ions, yielding weak solutions of carbonic, sulfuric, nitric, and hydrochloric acids. 3D model of hydrogen bonds between molecules of water. Two hydrogen atoms (white) and one oxygen atom (red) make up a water molecule. There are tiny electric charges (positive and negative) that cause the molecules to attract each other. Drawing by User Qwerter at Czech Wikipedia: Qwerter. Vectorized by Magasjukur2. https://commons.wikimedia.org/w/index.php?curid=14929959. 3D model of cellulose molecules, showing that they are made up of mainly hydrogen (white) and hydroxyl groups (red and white) bonded together with carbon (black) and oxygen (red). Like water molecules, the hydrogen and hydroxyl ions of cellulose molecules also have tiny electric charges (positive and negative). So, when water and cellulose molecules are in contact, they attract each other, drawing them closer together. Drawing by Ben Mills. https://commons.wikimedia.org/w/index. php?curid=6611880. As soon as rainwater percolates into the soil and the underlying rocks, it starts to dissolve whatever minerals are available so no spring water is pure but its contents will depend on the solubility of the minerals it passes through. Consequently, what we often think of as naturally pure water will often contain impurities, for example, copper and iron and, even occasionally in some areas, heavy metals like lead and arsenic. Rivers and streams are fed by surface-water runoff, springs, anthropogenic discharges (such as treated or untreated sewage and industrial effluent), and so-called baseflow (water derived from both shallow and deep subsurface flow). Consequently, these sources of water will not be pure and, indeed, they can be muddy or peaty or contain undesirable contaminants, depending on the surrounding land and any discharges in the area. Many small-scale papermakers may find that using the public supply is the easiest solution. While the public water supply should meet local statutory drinking standards, these can be enormously variable, even in a single country.2 Other local alternatives can be rainwater or you may have your own water well. The important point is that no water is entirely pure and may benefit from treatment. Apart from dissolved materials, untreated water may be turbid and contain micro-organisms; at Hayle Mill we very occasionally found freshwater shrimps! Because of the previously mentioned universal-solvent property, water can also dissolve a large variety of ions such as sulfate, copper, iron, and manganese that are readily available in the environment. These may be safe for us to consume at the generally very low levels detected, but harmful to paper. For most purposes your public water supply will be fine unless you want your paper to last a long time without discoloration, specks of debris, foxing, 3 and loss of strength. Wouldn't it be easy if you could just buy a simple test for water purity? You can buy many types of water-testing kits (either online or in your local garden or aquatic center) but I would not recommend them for papermaking. Even if you just wanted to check that the water is safe to drink, such tests have their limitations.4 My recommendation would be to undertake an online search for water-testing laboratories, ideally those that are accredited to the international standard ISO 17025. Typically these labs will provide you with one or more sample bottles for you to fill and return to them by post. Make sure they can test for the characteristics you are interested in, and that these analytical tests are appropriately certified. It may be useful to speak with them before you make a choice. Ask them if they will provide help interpreting the results. Knowing that your water has 1.3 parts per million of PCB may not, in itself, be very useful. Before you take the sample, let your supply pipe run free for, say, ten minutes and follow the supplier's instructions carefully. Be mindful of the state of your property's plumbing, as water may dissolve contaminants from your pipes and tanks, and you could find elevated levels of metals such as copper, zinc, and nickel, particularly if the pipework is old and starting to corrode. Many years ago, we needed to replace galvanized steel pipes at Hayle Mill and before deciding what with, I had the water tested in our cafeteria. This was because the final pipe-run from the public water supply was copper. I found that when the system was flushed through, no copper was detectable, but if the sample was taken after the water had been in the pipe overnight, 1 part per million of copper was found in the hard water. Copper (along with other metals commonly used in plumbing fixtures and fittings) will dissolve much more readily in soft or acidic water. We used high-density polyethylene pipe instead, but get advice on the best material today. What should you have tested? I would suggest as a minimum: - turbidity - suspended solids - total dissolved solids - total hardness - the potential of hydrogen (more commonly referred to as pH, which is a measure of how acidic or alkaline the water is) - aluminum, calcium, chlorine, copper, iron, magnesium, manganese, nitrate, potassium, sodium, and sulfate - bacteria (in particular, coliforms), and heavy metals such as arsenic, cadmium, chromium, lead, and selenium—these may not harm your paper but they could be bad for you! Modern analytical methods are so accurate that a laboratory can easily test for hundreds of different constituents to a precision of parts per billion. Understanding the results can be difficult which is why a lab that offers a short discussion with you could be helpful. Remember, though, that they are experts in water and not in paper. Ideally your water should be absolutely clear (lacking turbidity), colorless and odorless, have a neutral-to-alkaline pH, and have less than 1 part per million of aluminum, chlorine, copper, iron, manganese, nitrate, sodium, and sulfate; at the very least it should comply with the local drinking water regulations (many water companies will give you the average concentrations of a range of parameters in water provided to your area, so it is worth speaking to them first before paying for a sample of water to be analyzed). Not all dissolved minerals are harmful. If you are lucky, in my opinion, you will have a hard water supply containing calcium and/or magnesium. These substances will make the water slightly alkaline and leave a residue in the paper that will protect against acid contamination. Their presence will also indicate that the water has passed through limestone or chalk and this will often remove other elements such as iron and copper. In my travels, I have always asked papermakers about their water supply and it seems to be no coincidence to me that nearly all of the handmade-paper mills famed for their quality had hard water supplies. It is a good idea to file away safely the results of your water testing, and make sure you have the water re-tested every few years (ideally annually if this is affordable). At Hayle Mill our testing spanned nearly 100 years from 1887, and the results showed very little fluctuation over that period.7 Many water supplies need minimal or no treatment. Suspended solids and turbidity may be dealt with by simple filtration. If your water contains undesirable metals or is acidic, you may decide that it needs treatment for which you will need to get advice from specialists. I would suggest getting two or three opinions from consultants who do not supply water-treatment systems. Bear in mind that even rainwater, demineralized water, or distilled water may be slightly acidic (for example a pH of 6.0–6.5), and could benefit from the controlled addition of calcium or magnesium carbonate. Be careful to check the purity of such additives. Some calcium carbonate can be just ground chalk which may be contaminated. Water supply companies sometimes sell reprecipitated chalk which is usually its purest form. Microbial organisms can often be dealt with by an ultraviolet light system (but make sure that this is well maintained). Water leaves a papermill in three ways. Some is in the paper, some evaporates, and some is effluent. Please do not assume that because your operation is small, your dirty water is harmless. If you are cooking fiber, caustic soda and other chemicals in the effluent might be harmful to a watercourse, and you may not be allowed to discharge it to the public sewer. You may need to consider a miniature treatment plant or perhaps use it to water your grounds, if the sodium content is low enough.8 I encouraged this practice when I was consulting at papermaking operations in India and the Philippines. Khadi Papers in India uses their waste water on their mango farm!9 Most finished paper contains about 7 to 8 percent water but this varies according to the environment. As the water content fluctuates, the paper will expand and contract slightly, in the short term causing the waviness known at Hayle Mill as "huvver." In time, however, these movements relax and the paper flattens. But paper still remains a slightly watery affair. I am very grateful for the help that Dr. Robert Keirle gave me in the preparation and writing of this article. His expertise in the water industry was vital but any errors must be ascribed to me. I would also like to thank paper conservators Antoinette Dwan and Sarah Bertalan for their assistance. Gray-water filtration set-up to reclaim vat water from sheet formation at Fresh Press Agrifiber Paper Laboratory. Gray water is collected into the inductor tank (left), then pumped through a filter unit (polyester felt bag media), then stored in the holding tank (right) to be gravity fed or pumped to vat location in the studio. Not pictured is an in-line UV filter to eliminate bacteria. Courtesy of Steve Kostell, 2013. notes 1. "How much water is there on, in, and above the Earth?" on the US Geological Survey website, https://water.usgs.gov/edu/earthhowmuch.html (accessed November 6, 2017). 2. I have compiled extra information in a web supplement which is available on Hand Papermaking's website at http://handpapermaking.org/?p=2510. 3. For a very helpful article on foxing by paper conservator Sarah Bertalan, see the web supplement on Hand Papermaking's website, http://handpapermaking .org/?p=2510. 4. "Home Water Tests: The Claims, The Truth," on Good Housekeeping's website, gives an interesting overview of home water test kits on the market, though it is not a robust scientific study. http://www.goodhousekeeping.com/health-products/ a18919/water-tests/ (accessed November 6, 2017). 5. This international standard specifies the requirements for the competence to carry out testing, including sampling. https://www.iso.org/standard/39883.html (accessed November 6, 2017). 6. The term pH refers to the negative logarithm (base 10) of the activity of the hydrogen ion. On a scale of 0 to 14, solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic or alkaline. Ideally paper and the water it is made from should have a pH of 7 to just over 8. As the scale is logarithmic, water with a pH of 5.0 is twice as acidic as water with a pH of 6.0. 7. In circa 1990, I took a sample of water from the supply at the ancient mill at Pietrabuena, near Pescia in Tuscany. The results were remarkably close to those for Hayle Mill. 8. Although low levels of Na+ can be beneficial in many conditions, moderate and high levels of salt are detrimental to the majority of plants which is classified as glycophytic. Indeed, soil salinity is one of the prime abiotic stresses classified as glycophytic. Indeed, soil salinity is one of the prime abiotic stresses limiting agricultural production in many areas of the world. For more, see limiting agricultural production in many areas of the world. For more, see "Sodium in Plants" on the Journal of Experimental Botany website, https:// "Sodium in Plants" on the Journal of Experimental Botany website, https:// academic.oup.com/jxb/article/65/3/849/524705 (accessed February 13, 2018). academic.oup.com/jxb/article/65/3/849/524705 (accessed February 13, 2018). 9. For more on Khadi Papers environmentally conscious water-usage 9. For more on Khadi Papers environmentally conscious water-usage practices, go to http://khadi.com/about-khadi-papers/environment (accessed practices, go to http://khadi.com/about-khadi-papers/environment (accessed November 6, 2017). This water treatment system at Auroville Papers, India, helps to clean pigment November 6, 2017). This water treatment system at Auroville Papers, India, helps to clean pigment from vat water and gray water released during pressing. The system runs day and from vat water and gray water released during pressing. The system runs day and night and processes more than 800 liters of gray water per day. First, the gray water night and processes more than 800 liters of gray water per day. First, the gray water is collected in a tank. The sludge, including fiber and some pigments, is allowed to is collected in a tank. The sludge, including fiber and some pigments, is allowed to settle, then collected and composted, or given to another enterprise nearby that settle, then collected and composted, or given to another enterprise nearby that makes furniture with it. The remaining water goes into a baffle reactor, then is makes furniture with it. The remaining water goes into a baffle reactor, then is pumped three meters up into a cylinder that creates a vortex to remove further pumped three meters up into a cylinder that creates a vortex to remove further particles (pictured top left). The water is then gravity fed down through 15 concrete particles (pictured top left). The water is then gravity fed down through 15 concrete pods, called flow forms (pictured top right). The force of the water movement helps pods, called flow forms (pictured top right). The force of the water movement helps to clean the water which then flows into the garden along sharp curves and loops to clean the water which then flows into the garden along sharp curves and loops through two successive "swamps" where the roots of plants help to further clean through two successive "swamps" where the roots of plants help to further clean the water, binding up the pigments. The fiber-rich plants are supported by and the water, binding up the pigments. The fiber-rich plants are supported by and grown on the islands (not in soil); and the plants are regularly harvested to be used grown on the islands (not in soil); and the plants are regularly harvested to be used in papermaking workshops at the mill. The water is also used to wash fiber prior in papermaking workshops at the mill. The water is also used to wash fiber prior to processing into pulp. Courtesy of Auroville Papers, India, with the assistance of to processing into pulp. Courtesy of Auroville Papers, India, with the assistance of Radha Pandey. Radha Pandey.