《中黄秘诀》曰∶阴生水，水性常冷，而有华阳温泉濡之，不胜其暖也。阳生火，火性常热，而有
萧丘寒焰向之，终不能暖也。外之水火，尚有返复之性；内之阴阳，安无颠倒之宜？如肾，水也。水中生
气，气为火矣。心，火也。火中生液，液为水矣。水可以滋流百脉，火可以薰蒸四大。人之水火也，如此。
《通玄论》曰∶道原一判而分二仪，天以干道而轻清在上。在上以阳为用，暗抱一点真阴在其
中也。故冬至后，地中阳生，夏至到天。积阳所以生阴，其阴感阴而阴不得耗散，散为雾，凝为露，雾露
之气，天之所出阴而真水也。地以坤道而重浊在下。在下以阴为用，暗抱一点真阳在其中也。故夏至后，
天中阴降，冬至到地。积阴所以生阳，盖其阳感阳而阳不散耗，升为云，施为雨，云雨之气，地之所出阳
而真火也。人亦若是。受胎之初，父精母血，二气相合。阳气上升，心为气馆，气中暗藏，真水在心也。
阴气下降，肾为水府，水中暗藏，真气在肾也。不然，安得肾气到心，积气生液，一阴生于二阳之中；心气
到肾，积液生气，一阳升乎二阴之中也？
《西山记》曰∶凡人有三火八水。水者，一气传一气，积气生液，而五脏各有液，名曰色水。
肾气之中，暗藏真一之水，而为阴虎者，名曰真水。肘后飞金晶入上宫，自上而下，与
真火相逢，而既济成，然名曰神水。凡有疾病，闭口纳气，一口复一口，定中送在病处，皆可痊安，
名曰法水。水之为用多矣，其名不一。丹就真气生，灌溉而为沐浴之法，炼形真气升，还返而为还丹
之法。刘海蟾言∶两曜注成七宝殿，一渠流转八琼浆。是玉液还丹也。吕公言∶水火都来相作间，卦候飞
成地天泰。一升一沉阳炼阴，阴尽方知此理深。是上下水火既济之候也。逍遥子曰∶法水能朝有秘关，
逍遥日夜遣循环。是法水治病也。此水之大概矣。三火者，膀胱民火，肾为臣火，心为君火。凡所无
知，为物所扰而怒且忧者，则为无明之火。若降而下烧丹田，一意不散，至诚守之，而曰烧炼丹药。
火之升上，起后过双关，而曰河车。升之前起上过重楼，而曰炼形。前后俱起，遍满四大，炎炎焚
身，此火之大概矣。
《九仙经》曰∶病小用水，病大用火。病大者，无常之限也。若人误犯天神，或身不宁，急入静
室，散发拨衣，闭目冥心，正坐握固，叩齿集神，升身起火，微以留息，少入迟出，默想如脐下火轮大如
斗，须臾焰起自身，可比轮盖，罩定自身，令阴鬼邪魔不敢近也。释教降魔火，道家焚身火。凡
行此火，须是久绝嗜欲，丹元坚固。不然，以水火交媾，龙虎成丹，丹就而阴灵自散，不敢近阳，神自
不肯去也。神在形固，阴退气全，气全角坚，自可长年。
《中黄秘诀》说：阴产生水，水的本性通常是寒冷的，但如果有华阳温泉来滋润它，就抵挡不住它的温暖了。阳产生火，火的本性通常是炎热的，但如果有萧丘的寒焰对着它，终究不能使它变暖。外在的水和火，尚且有反复变化的性质；内在的阴和阳，难道没有颠倒转化的适宜道理吗？比如肾，属于水。水中产生气，气就变成了火。心，属于火。火中产生液，液就变成了水。水可以滋养流淌百脉，火可以熏蒸全身（四大）。人的水火关系，就是这样的。
《通玄论》说：道的本源一分为二，形成天地两仪，天遵循乾道而轻清上升在上。在上位以阳为作用，暗中抱持一点真阴在其中。所以冬至以后，地中阳气开始生发，直到夏至积累到极点从而产生阴气，这阴气感应阴气而不耗散，散发成为雾，凝结成为露，雾露之气，是天所发出的阴，也就是真水。地遵循坤道而重浊下降在下。在下位以阴为作用，暗中抱持一点真阳在其中。所以夏至以后，天上阴气开始下降，直到冬至到达地面。积累阴气从而产生阳气，大概是因为阳气感应阳气而不分散耗损，上升成为云，施降成为雨，云雨之气，是地所发出的阳，也就是真火。人也像这样。在受孕之初，父亲的精和母亲的血，两种气相合。阳气上升，心作为气的馆舍，气中暗藏真水在心。阴气下降，肾作为水的府库，水中暗藏真气在肾。如果不是这样，怎么能使得肾气上升到心，积累气产生液，在一阴生于二阳之中；心气下降到肾，积累液产生气，一阳升于二阴之中呢？
《西山记》说：大凡人有三火八水。水方面，是一气传一气，积气生液，而五脏各有液，名叫色水。肾气之中，暗藏真一之水，作为阴虎的，名叫真水。通过肘后飞金晶的方法进入上宫，自上而下，与真火相逢，从而既济成功，名叫神水。凡是患有疾病，闭口纳气，一口接一口，在定境中送到病处，都可以痊愈平安，名叫法水。水的作用很多，名称不一。丹药炼成后真气生发，灌溉身体作为沐浴之法；炼形时真气上升，返还身体作为还丹之法。刘海蟾说：“两曜注成七宝殿，一渠流转八琼浆。”这是玉液还丹。吕公说：“水火都来相作间，卦候飞成地天泰。一升一沉阳炼阴，阴尽方知此理深。”这是上下水火既济的征候。逍遥子说：“法水能朝有秘关，逍遥日夜遣循环。”这是法水治病。这是关于水的大概情况。三火方面，膀胱为民火，肾为臣火，心为君火。凡是无所不知，被外物干扰而愤怒且忧愁的，就是无明之火。如果降下并烧向丹田，意念不散，至诚守之，就叫烧炼丹药。火气升上，经过后面的双关，就叫河车。升起之前经过上面的重楼，就叫炼形。前后都升起，遍满全身，炎炎燃烧身体，这是关于火的大概情况。
《九仙经》说：小病用水，大病用火。所谓大病，是指无常的期限（死亡）。如果有人误犯天神，或者身体不安宁，急忙进入静室，披散头发，解开衣服，闭上眼睛冥想内心，端正坐姿握紧拳头（握固），叩齿聚集精神，提升身体发起火，微微留息，少量吸入缓慢呼出，默想脐下的火轮大如斗，一会儿火焰从自身升起，可比拟轮盖，罩住自身，令阴鬼邪魔不敢靠近。佛教的降魔火，道家的焚身火。凡是施行这种火法，必须长久断绝嗜好欲望，丹元坚固。不然的话，以水火交媾，龙虎结成丹药，丹药炼成而阴灵自然消散，不敢靠近阳气，神灵自然不肯离去。神灵在形体稳固，阴气退去气机完整，气机完整则骨角坚硬，自然可以长寿。
The *Zhonghuang Mijue* (Secrets of the Middle Yellow) states: Yin generates Water, and the nature of Water is usually cold; yet if it is moistened by the Hua Yang Hot Spring, it cannot withstand its warmth. Yang generates Fire, and the nature of Fire is usually hot; yet if the Xiao Qiu Cold Flame faces it, it ultimately cannot become warm. External Water and Fire still possess the nature of reversal and change; how much more so should Internal Yin and Yang have the appropriateness of inversion and transformation? For instance, the Kidney is Water. Within Water, Qi arises, and Qi becomes Fire. The Heart is Fire. Within Fire, Fluids are generated, and Fluids become Water. Water can nourish and flow through the hundred vessels; Fire can steam and vaporize the Four Elements (the physical body). Thus, the relationship between Water and Fire in humans is as follows.
The *Tongxuan Lun* (Discourse on Communicating with the Profound) states: The origin of the Dao splits into one to form two Yi (Heaven and Earth). Heaven follows the Qian Way, being light and clear, ascending above. In the upper position, Yang serves as function, secretly embracing a point of True Yin within it. Therefore, after the Winter Solstice, Yang arises within the earth, accumulating until the Summer Solstice, where accumulated Yang generates Yin. This Yin, sensing Yin, does not dissipate; it scatters as mist and condenses as dew. The qi of mist and dew is what Heaven emits as Yin, which is True Water. Earth follows the Kun Way, being heavy and turbid, descending below. In the lower position, Yin serves as function, secretly embracing a point of True Yang within it. Therefore, after the Summer Solstice, Yin descends from heaven, reaching the earth at the Winter Solstice. Accumulated Yin generates Yang. Presumably, this Yang, sensing Yang, does not scatter or dissipate; it rises as clouds and manifests as rain. The qi of clouds and rain is what Earth emits as Yang, which is True Fire. Humans are likewise. At the beginning of conception, the father’s essence and the mother’s blood combine. Yang Qi ascends, and the Heart serves as the residence of Qi; within this Qi, True Water is secretly hidden in the Heart. Yin Qi descends, and the Kidney serves as the mansion of Water; within this Water, True Qi is secretly hidden in the Kidney. Otherwise, how could Kidney Qi ascend to the Heart, accumulating Qi to generate Fluids, allowing one Yin to arise from within two Yangs? And how could Heart Qi descend to the Kidney, accumulating Fluids to generate Qi, allowing one Yang to rise from within two Yins?
The *Xishan Ji* (Record of Western Mountain) states: Ordinary people possess Three Fires and Eight Waters. Regarding Water: One Qi transmits to another Qi, accumulating Qi to generate Fluids, and each of the Five Zang Organs has its own Fluid, named Se Water (Color Water). Within Kidney Qi, there is secretly hidden True One Water, acting as the Yin Tiger, named True Water. Through the method of "Flying Golden Crystal from the Back of the Elbow" entering the Upper Palace, moving from top to bottom, meeting with True Fire, thereby achieving Ji Ji (Mutual Completion), it is named Divine Water. Whenever there is disease, closing the mouth and swallowing Qi, breath after breath, sending it to the diseased area in a state of stillness, all can recover and be at peace, named Method Water. The uses of Water are numerous, and its names vary. When the Elixir is formed, True Qi arises, irrigating the body as the Bathing Method; when refining the Form, True Qi ascends, returning to the body as the Returning Elixir Method. Liu Haichan said: "Two luminaries pour into the Seven Treasures Hall, one channel flows with the Eight Jade Nectar." This refers to the Jade Fluid Returning Elixir. Master Lü said: "Water and Fire come together to interact, the hexagram phases fly to form Di Tian Tai (Heaven-Earth Peace). One ascends, one descends, Yang refines Yin; only when Yin is exhausted do we know the depth of this principle." This refers to the phase of mutual completion of upper and lower Water and Fire. Xiaoyaozi said: "Method Water can face the secret pass, wandering day and night dispatching circulation." This refers to Method Water treating diseases. This is the general overview of Water. Regarding the Three Fires: the Bladder is the People’s Fire, the Kidney is the Minister’s Fire, and the Heart is the Sovereign’s Fire. Any ignorance, disturbance by external objects leading to anger and sorrow, constitutes the Fire of Ignorance (Avidya). If this fire descends and burns the Dantian, with undivided attention and sincere preservation, it is called burning and refining the medicinal elixir. When Fire Qi ascends, passing through the Double Pass behind, it is called the River Vehicle (He Che). Before rising, passing through the Heavy Tower above, it is called refining the Form. When both front and back rise, filling the Four Elements, blazing and burning the body, this is the general overview of Fire.
The *Jiuxian Jing* (Scripture of Nine Immortals) states: Use Water for minor illnesses, use Fire for major illnesses. A major illness refers to the limit of impermanence (death). If someone mistakenly offends the Heavenly Spirits, or feels bodily unrest, they should urgently enter a quiet room, let down their hair, loosen their clothes, close their eyes and meditate inwardly, sit upright with hands clenched (Wogu), click the teeth to gather spirit, raise the body to initiate Fire, retain the breath slightly, inhale little and exhale slowly, and visualize a fire wheel under the navel as large as a dou (a unit of measure). Suddenly, flames rise from the body, comparable to a wheel cover, enveloping the self, preventing yin ghosts and evil spirits from approaching. The Buddhist Demon-Subduing Fire, the Daoist Body-Burning Fire. To practice this Fire method, one must long have cut off desires and passions, ensuring the Dan Yuan (Elixir Field) is firm. Otherwise, through the coitus of Water and Fire, Dragon and Tiger forming the Elixir, once the Elixir is formed, the Yin Spirit naturally dissipates, daring not approach Yang, and the Shen (Spirit) naturally refuses to leave. With Shen present and the Form solid, Yin retreats and Qi becomes complete; with Qi complete, the bone angles become firm, thus enabling longevity.