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Jala vijnana (Samskrit: जलविज्ञानम्) is the science of water, referred to as Hydrology in modern parlance. Ancient samskrit literature contains the most valuable and highly advanced scientific discourses on hydroscience, sadly unexplored to a great extent. Natural forces such as the sun, moon, earth, rivers, ocean, wind, rain, water, agni have been worshipped both as physical entities as well as deities who played significant role in srsthi (creation) and sthiti (maintenance). 

In vedas one can find references to the concept of loosely bound water molecules; Puranas mention that water is not created or destroyed and it undergoes a change of state through the various phases of water cycle. Earliest references to the process of raindrop formation, rainfall patterns, astronomical factors that affect rains, the chemical aspects such as evaporation, condensation, cloud formation, precipitation are all found interspersed in ancient texts, depicting the technological advancement of Bharatavarsha.<ref name=":1" />

== Introduction ==
Effects of Yajnas (in causing rains), forests, reservoirs, classification of clouds, their color, rainfall capacity etc, forecasting of rainfall on the basis of natural phenomena like color of the sky, clouds; wind direction, lightening, and the activities of animals was well developed in ancient days. Varshamapana yantra (rain guage) a contrivance to measure rainfall was referred in Arthashastra of Kautilya and Ashtadhyayi of Panini. The modern hydrology evaluations are based on the ancient technology used in such yantras differing in the weight measure (of Drona and Pala) instead of the modern linear measurement of rainfall. The quantity of rainfall in various parts of Bharat was also predicted by Kautilya.<ref name=":1">''[https://www.indiawaterportal.org/sites/indiawaterportal.org/files/hydrology_in_ancient_india_nih_1990.pdf Hydrology in Ancient India]'' by National Institute of Hydrology, Roorkee, India (1990)</ref>

Brhat samhita discusses the ground water development and water quality methods. Driven by sound concepts, people of ancient Bharat could locate groundwater, analyze its distribution and had knowledge of reaching these water-tables to irrigate fields.

== States of Water ==
The three states of water are liquid, solid (ice) and vapour (steam). Linga Purana explains that water cannot be destroyed and only its state is changed.<blockquote>तोयस्य नास्ति वै नाशः तदैव परिवर्तते॥ ५४.३३॥ (Ling. Pura. 54.33)<ref>Linga Purana ([https://sa.wikisource.org/wiki/%E0%A4%B2%E0%A4%BF%E0%A4%99%E0%A5%8D%E0%A4%97%E0%A4%AA%E0%A5%81%E0%A4%B0%E0%A4%BE%E0%A4%A3%E0%A4%AE%E0%A5%8D_-_%E0%A4%AA%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%B5%E0%A4%AD%E0%A4%BE%E0%A4%97%E0%A4%83/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0% Purvabhaga, Adhyaya 54])</ref></blockquote>

== Hydrology ==
Hydrology involves the study of flowing water bodies, change of water states and other elements of hydrology and water resources as follows 
* Hydrologic or Water Cycle 
* Precipitation, cloud formation, measurement etc.
* Interception and Infiltration
* Surface Water
* Ground Water
* Water Quality and Purification
* Water use and conservation.
A few of these topics are discussed below.

=== Water Cycle ===
The Hydrological or Water Cycle is an important concept in hydroscience. It is the chain of events describing the movement of water involving the total earth system comprising of the atmosphere (the gaseous envelop), the hydrosphere (surface and subsurface water), lithosphere (soils & rocks), and the biosphere (plants & animals). In one of the three phases (solid, liquid, and vapour) the water passes through these four parts of the earth system.

==== Evaporation ====
A number of mantras in the Rigveda support the fact that our ancient rshis and maharshis have thorough knowledge of the water cycle and processes involved.  
* आदह स्वधामनु पुनर्गर्भत्वमेरिरे। दधाना नाम यज्ञियम्॥४॥ (Rig. Veda. 1.6.4) Water which gets divided in minute particles due to the heat of the sun is carried by wind and after the conversion into cloud it rains again and again. Rigveda (1.19.7) also reiterates the transfer of water from earth to the atmosphere by the wind. 
* इन्द्रो दीर्घाय चक्षस आ सूर्यं रोहयद् दिवि। वि गोभिरद्रिमैरयत्॥३॥ (Rig. Veda. 1.7.3) Just as the sun is created and placed such as to illuminate the whole universe, so also as a rule of universe, it extracts water continuously to convert it to cloud and ultimately discharge as rain. Rig veda (1.23.17) also supports this concept.  
Yajurveda also discusses the water cycle as follows, the movement of water from from clouds to earth and its flow through channels and storage into oceans and further evaporation.<blockquote>प्र पर्वतस्य वृषभस्य पृष्ठान्नावश्चरन्ति स्वसिचज्ञयानाः । ता आववृत्रन्नधरागुदक्ता अहिं बुध्न्यमनु रीयमाणाः । विष्णोर्विकर्मणम् असि । विष्णोर्विक्रान्तम् असि । विष्णोः क्रान्तम् असि ॥ (Shuk. Yaju. Veda. 10.19)<ref>Shukla Yajurveda ([https://sa.wikisource.org/wiki/%E0%A4%B6%E0%A5%81%E0%A4%95%E0%A5%8D%E2%80%8D%E0%A4%B2%E0%A4%AF%E0%A4%9C%E0%A5%81%E0%A4%B0%E0%A5%8D%E0%A4%B5%E0%A5%87%E0%A4%A6%E0%A4%83/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A7%E0%A5%A6 Adhyaya 10])</ref></blockquote>

==== Cloud Formation ====
Water cycle is described in the Vaiseshika Sutras. Watery vapors closer to the earth in combination with sun's rays ascend upwards into the sky forming clouds. The Vaiseshika Sutras by Kanada clearly mention the interactions of these particles as follows<blockquote>नाड्या वायुसंयोगादारोहणम् । वैशेषिक-५,२.५ । नोदनापीडनात् संयुक्तसंयोगाच्च । वैशेषिक-५,२.६ । वृक्षाभिसर्पणमित्यदृष्टकारितम् । वैशेषिक-५,२.७ । (Vais. Sutr. 5.2.5-7)</blockquote>Further to the rising of water vapour, cloud formation, lightning and thunder are explained in the Vaiseshika sutras and bhashya as follows<blockquote>अपां सङ्घातो विलयनं च तेजः संयोगात् । वैशेषिक-५,२.८ । तत्र विस्फूर्जतुर्लिङ्गम् । वैशेषिक-५,२.९ । वायुसंयुक्तास्सूर्यरश्मयः अपः भूमिष्ठास्तावदन्तरिक्षमारोहयन्ति ।। (Vais. Sutr. 5.2.8-10) </blockquote><blockquote>अन्तरिक्षमारूढाः खल्वापः धूमेन ज्योतिषा वायुना च संसृज्यमानाः मेघभावमापद्यन्ते (Form clouds) | </blockquote>Water rising (in the form of vapor) by combining with the smoke, heat (of the sun's rays) and winds (in the upper strata) form the Clouds. <blockquote>जले दिव्यज्योतिस्संयोगे सति विद्युत्प्रकाशः (Lightning) ततो विस्फूर्जथुः (Thunder) | </blockquote>Kalidasa also poetically mentions the formation of clouds in his Meghadoota.<blockquote>धूमज्योतिस्सलिलमरुता सन्निपातः क्व मेघः । (Megh. 5)</blockquote>

==== Clouds and Rainfall ====
As food is the elixir of life to living beings, and as food is dependent on the monsoon, it should be investigated carefully. He explains the exceptional ability of predicting exact time of rainfall with the help of astrological sciences. A good astrologer who observes the skies and cloud formation, with the knowledge of planetary positions and [[Nakshatras (नक्षत्राणि)|nakshatras]] can accurately predict the rainfall according to Varahamihira.  <blockquote>मार्गशिरःसितपक्षप्रतिपत्प्रभृति क्षपाकरेऽषाढाम् । पूर्वां वा समुपगते गर्भाणां लक्षणं ज्ञेयम् ।। २१.०६ ।। (Brhd. Samh. 21.6)<ref name=":0">Brhat Samhita ([https://sa.wikisource.org/wiki/%E0%A4%AC%E0%A5%83%E0%A4%B9%E0%A4%A4%E0%A5%8D%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A8%E0%A5%A7 Adhyaya 21])</ref></blockquote>Meaning: Know that the characteristics of pregnancy of clouds (in the sense of formation of rain-bearing clouds) are to be observed when moon transits Purvashada nakshatra commencing from Margasira Shukla paksha.  

Thus an astrologer starts observing the skies (for the formation of clouds) from that day of the bright half of Margasira month when moon transits Purvashada nakshatra. The cloud fetus so formed during the moon's stay in a particular asterism (nakshatra) will be delivered (in the sense of rainfall) 195 days (savana day) after the fetus formation, when the moon transits the same nakshatra (this usually falls in the months of Jyesta and Ashadha, the rainy seasons) as given  in the shloka below. <blockquote>यन्नक्षत्रं उपगते गर्भश्चन्द्रे भवेत्स चन्द्रवशात् ।  पञ्चनवते दिनशते तत्रएव प्रसवं आयाति ।। २१.०७ ।। (Brhd. Samh. 21.7)<ref name=":0" /></blockquote>

==== Evaporation, Condensation and Precipitation ====
In Matsya Purana (1.54.29-34) and Vayu Purana, we come across the description about evaporation, rising of water vapor, condensation and precipitation.<blockquote>सर्वभूतशरीरेषु आपो ह्यनुगताश्च याः । तेषु सन्दह्यमानेषु जङ्गमस्थावरेषु च। धूमभूतास्तु ता आपो निष्क्रामन्तीह सर्वशः ।। ५१.२२ ।।</blockquote><blockquote>तेन चाभ्राणि जायन्ते स्थानमत्राम्भसां स्मृतम् । आर्कन्तेजो हि भूतेभ्यो ह्यादत्ते रश्मिभिर्जलम् ।। ५१.२३ ।।</blockquote><blockquote>समुद्राद्वायुसंयोगाद्वहन्त्यापो गभस्तयः। यतस्त्वृतुवशात् काले परिवर्त्तो दिवाकारः। यच्छत्यपो हि मेघेब्यः शुक्लाः शुक्लगभस्तिभिः ।। ५१.२४ ।।</blockquote><blockquote>अभ्रस्था प्रपतन्त्यापो वायुना समुदीरिताः। सर्वभूतहितार्थाय वायुभिश्च समन्ततः ।। ५१.२५ ।।</blockquote><blockquote>ततो वर्षति षण्मासान् सर्वभूतविवृद्धये। वायव्यं स्तनितञ्चैव वैद्युतञ्चाग्निसंभवम् ।। ५१.२६ ।। (Vayu. Pura. 51.23-26)<ref>Vayu Purana ([https://sa.wikisource.org/wiki/%E0%A4%B5%E0%A4%BE%E0%A4%AF%E0%A5%81%E0%A4%AA%E0%A5%81%E0%A4%B0%E0%A4%BE%E0%A4%A3%E0%A4%AE%E0%A5%8D/%E0%A4%AA%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%B5%E0%A4%BE%E0%A4%B0%E0%A5%8D%E0%A4%A7%E0%A4%AE%E0%A5%8D/%E0%A4%85%E0%A4%A7%E0%A5 Purvardha, Adhyaya 51])</ref></blockquote>Summary: Water is present in the bodies of all living beings. When the bodies of the mobile and immobile beings (plants and trees) burn, the water becomes vapour and rises from all sides. The clouds arise thereby (by the collection of this vapor) as they are the receptacles of water. The brilliance of the sun takes up the water from the living beings through the rays. Water is also taken up from the oceans by the winds and sun-rays. The changing movements of the sun, during appropriate times with seasons, water is imparted to the clouds by means of his white rays. When blown by the wind, the water drips from the clouds. The clouds shower for six months in order to nourish and develop all living beings. They produce the rumbling sound of thunder arising from the wind and brilliant lightning arising from fire.<ref>Tagare, G. V., (1987) ''The Vayu Purana, Part 1.'' Delhi: Motilal Banarsidass (Page 349)</ref>

Here the puranic references of water cycle clearly explain the scientific processes  of evaporation, formation of clouds, precipitation, the thunder and lightnings. Varahamihira's Brhat Samhita extensively discusses about hydrometrology comprising of Pregnancy of clouds (Adhyaya 21), Pregnancy of air (Adhyaya 22) and quantity of rainfall (Adhyaya 23).<ref name=":1" />

==== Rain Gauges ====
Rain gauging was prevalent in India even before Panini (3.4.32) who provides for terms referring to measures of rainfall. The Arthashastra (2.5.7) describes the rain-gauge as a basin with a mouth one aratni (= 24 ahgulas) in width. According to the Brhatsamhita (23.2) the raingauge is to be one hasta or cubit (18 inches) in diameter. When filled to the brim it indicates 50 palas or 1 aadhaka of rainfall. Other texts like Krshiparasara, differ in the measurement of 1 aadhaka and other measures such as drona and dhanus.

Rtuvijnana or climatology developed along with astronomy. The Brhatsamhita, the most standard work of this type, has many chapters dealing with several aspects of the subject. Varahamihira himself refers to some earlier authorities, but their writings are not available in their original form.<ref name=":12">Bag, A. K. (1997) ''History of Technology in India, Vol. 1, From Antiquity to c. 1200 A.D.'' New Delhi: Indian National Science Academy. (Pages 417 - 432)</ref>

=== दकार्गलम् ॥ Exploration of Water Springs ===
Dakargalam, mean "Water-finding" (also called Jalargalam or Udakargalam), pertains to the science of exploration of water springs or underground water resources (जलौपलब्धिज्ञानम्). Brhat Samhita the celebrated book of Varahamihira is a treasure trove of ancient Bharat's technical advancements written in the early christian era. In here we find the detailed explanation about exploration of water veins beneath the earth's surface.<blockquote>धर्म्यं यशस्यं च वदाम्यतोऽहं दकार्गलं [क्.दगार्गलं] येन जलौपलब्धिः ।  पुंसां यथाङ्गेषु शिरास्तथैव क्षितावपि प्रोन्नतनिम्नसंस्थाः ।।</blockquote><blockquote>एकेन वर्णेन रसेन चाम्भश्च्युतं नभस्तो वसुधाविशेषात् । नानारसत्वं बहुवर्णतां च गतं परीक्ष्यं क्षितितुल्यमेव ।। (Brhat. Samh. 54.1-2)</blockquote>Meaning: I shall now explain the science of water-finding which is dharmika and brings renown, for it helps men to ascertain the existence of water. Just as there are veins in the human body, even so they exist, some higher up and some lower in the earth. The water that falls from the sky with the same color and taste, assumes various colors and tastes owing to the difference in the nature of the earth.<ref>Pt. V. Subrahmanya Sastri and M. Ramakrishna Bhat (1946) ''Varahamihira's Brihat Samhita with an English Translation and Notes.'' Bangalore: Electronic Printing Works. (Pages 458 and 459)</ref>

Varahamihira speaks of eight underground arteries of water, four flowing in the four cardinal points and four in the intermediate directions with a ninth which shoots upward (verses 3-6). He takes the presence of certain trees and ant-hills in different directions of specified trees as indicating underneath water at a waterless place (ambu-rahita).<blockquote>पुरुहूतानलयमनिरृतिवरुणपवनैन्दुशङ्करा देवाः । विज्ञातव्याः क्रमशः प्राच्यऽद्यानां दिशां पतयः ।। ५३.०३ ।।</blockquote><blockquote>दिक्पतिसंज्ञा च शिरा नवमी मध्ये महाशिरानाम्नी । एताभ्यो +अन्याः शतशो विनिःसृता नामभिः प्रथिताः ।। ५३.०४ ।।</blockquote><blockquote>पातालाद्*ऊर्ध्वशिरा शुभा[क्.ऊर्ध्वशिराः शुभाश्] चतुर्दिक्षु संस्थिता याश्च । कोणदिगुत्था न शुभाः शिरानिमित्तान्यतो वक्ष्ये ।। ५३.०५ ।। </blockquote><blockquote>यदि वेतसो अम्बुरहिते देशे हस्तैस्त्रिभिस्ततः पश्चात् । सार्धे पुरुषे तोयं वहति शिरा पश्चिमा तत्र ।। ५३.०६ ।। (Brhat. Samh. 53.3-6)<ref>Brihat Samhita ([https://sa.wikisource.org/wiki/%E0%A4%AC%E0%A5%83%E0%A4%B9%E0%A4%A4%E0%A5%8D%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%AB%E0%A5%A9 Adhyaya 53])</ref></blockquote>He mentions the depth at which water will be available, the nature of the water, the direction in which it flows, the type of stones and soil to be met at different levels and fish, frogs, rats, snakes and tortoise to be noticed (verses 6-85). The depth at which water is indicated for a desert land (marudesa) is not applicable to a jangala land (with little water). In the case of anupa land (with much water), if certain specified trees are found in ant-hills, then water will be at a distance of three persons length (purusas), in jangala land at a distance of five purusas and in maru land at a distance of seven purusas (verses 86-89). There are general indications of the presence of water in the form of colour and nature of soil, availability of vegetation on them, and the presence of anthills and insects without home (verses 90-96).<ref name=":12" />

=== Surface Water ===
Surface water bodies such as canals, ponds, wells, dams, tanks, lakes and rivers carried great importance since ancient times for providing water both for consumption and irrigation of fields. Construction of wells, lakes and ponds were considered as great acts of charity as jaladana was considered as an act of punya. 

=== Water Uptake in Plants ===
In Mahabharata, Shanti Parva we find references to how plants 'drink' water through their roots. The mechanism of water uptake by plants is explained by the example of water rising through a pipe. It is said that the water uptake process is facilitated by the conjunction of air.<ref name=":1" /><blockquote>पादैः सलिलपानाच्च व्याधीनां चापि दर्शनात्। व्याधिप्रतिक्रियत्वाच्च विद्यते रसनं द्रुमे।। (Maha. Shan. Parv. 12.184.15)</blockquote><blockquote>वक्रेणोत्पलनालेन यथोर्ध्वं जलमाददेत्। तथा पवनसंयुक्तः पादैः पिबति पादपः।। (Maha. Shan. Parv. 12.184.16)</blockquote>Plants drink water through their roots; when they are afflicted with any disease they are treated by addition of medicine at the roots which cures them. This shows that they have the sense of taste (rasanendriya). Just like a person can draw water from the pipelike lotus stalk by the suction force of air, so also plants plants can draw up the water from its roots to the leaves with the help of air (like a pipe).<ref>Pt. Ramnarayanadatt Shastri () ''Mahabharata, Volume 5, Shanti Parva. Hindi Translation.'' Gorakhpur: Gita Press (Page 4894)</ref>

== Water Purification Practices ==
It is also interesting to note that there existed several methods for assessing and maintaining water quality and also treatment methods as revealed by the Vedas and also books on "Ayurveda". In Brihat-Samhita, written and compiled by Varahamihira, several methods for obtaining potable water from contaminated sources, using plants, metals and heat are described besides the purification process of ground water has been dealt with at length.<ref name=":2">S. Manasi and K. V. Raju (2012) ''Water - A Heritage Perspective.'' </ref>

A powder mix extracted from herbs like Anjan, Bhadramustha, Khas (vetiver), Amla (emblica officinalis, gooseberry) and Nirmali (bhui amla / kataka), was in use in measured quantities for purifying water in wells. Sushruta, the famous Indian physician provided a detailed practical guidance for water purification. He showed that with herbs and other natural substance muddy water could be purified, using Nirmali seeds, roots of Kamal (lotus/water lily), rhizomes of algae and three stones, Gomed (garnet) Moti (pearl) and Sphatik (quartz crystal). He suggested exposing contaminated water to the sun or immersing a red hot iron rod or hot sand in it, for purification purpose.<ref name=":2" />
{| class="wikitable"
|+Traditional Practices of safeguarding drinking water
!Use of Alum in Water
|Aluminium sulfate or Alum is used as an aflocculant for removing unwanted colour and turbidity from water supplies. It has been used since ancient times for this purpose and its use together with filtration is a standard practice in conventional water treatment processes around the world.
|-
!Using cloth for filtering
|In Dhoti method, a thin piece of cloth is used for filtering water 
|-
!Keeping Tortoises in open wells 
|Tortoises are known to have a much longer life span than humans. It has been a traditional practice particularly in India to keep tortoises in drinking water wells so that they feed on organisms harmful to humans while keeping water safe for drinking.
|-
!Use of Moringa Seeds
|Moringa tree seeds are crushed into powder and used as a water-soluble extract in suspension, resulting in an effective natural purification agent for highly turbid and untreated pathogenic surface water.
|-
!Rain water harvesting
|Harvesting rain water through simple filtration methods such as using cloth pieces. 
|-
!Combination of local plant and filtration methods
|Raw water is filtered through powdered seeds of local plant materials including Moringa oleifera and Phyllanthus emblica—natural flocculants—and through coarse sand, charcoal, and gravel, which reduce the total aerobic mesophilic bacterial, E coli, coliform, pseudomonas, and yeast counts, and turbidity, consistent with World Health Organization acceptable standards for potable water.
|-
| colspan="2" |Source: <nowiki>http://hopebuilding.pbworks.com/w/page/19222829/Tamil-Nadu-group-finds-simple-way-to-purifydrinking-water</nowiki>
|}
It has been scientifically proved by researches that storing drinking water in brass vessels is good for health, a system which was also in practice in ancient times.

== Reference ==
[[Category:Shastras]]
<references />