Water lab­o­ra­to­ry analy­ses

General information

Ground­wa­ter is a com­plex nat­ur­al solu­tion that con­tains min­er­als, gas­es, organ­ic com­pounds, sus­pend­ed par­ti­cles, and microor­gan­isms. The min­er­al com­po­si­tion dom­i­nates and deter­mines the type of chem­i­cal com­po­si­tion of ground­wa­ter. Min­er­al com­po­nents are divid­ed into macro­scop­ic, micro­scop­ic, meta­phys­i­cal, and radioac­tive. The con­tent of gas com­po­nents is small and char­ac­ter­izes the speci­fici­ty of water com­po­nents. Organ­ic com­pounds include com­plex com­pounds such as phe­nols, organ­ic acids, hydro­car­bons, bitu­mens, humus, and oth­ers. Addi­tion­al­ly, a pletho­ra of var­i­ous organ­isms live in ground­wa­ter. The prop­er­ties and con­di­tion of water are stud­ied using lab­o­ra­to­ry meth­ods through sam­pling for chem­i­cal, gas, and organ­ic analy­ses, which are con­duct­ed by var­i­ous meth­ods on-site and under fixed con­di­tions (in a lab­o­ra­to­ry) if pos­si­ble direct­ly by test­ing the sources, wells, and bore­holes with spe­cial equip­ment.

Chem­i­cal analy­sis uses meth­ods based on the chem­i­cal reac­tions of the sub­stances under study (e.g. gravi­met­ric analy­sis and titra­tion). Physic­o­chem­i­cal meth­ods of chem­i­cal analy­sis are based on the mea­sure­ment of phys­i­cal quan­ti­ties whose changes are caused by chem­i­cal reac­tions (poten­tio­met­ric and amper­o­met­ric titra­tion). Phys­i­cal meth­ods pro­vide for the mea­sure­ment of phys­i­cal prop­er­ties that are deter­mined by the chem­i­cal prop­er­ties of the sub­stance.

The range of water used in dai­ly life is diverse and includes drink­ing and cook­ing, bathing, prop­er func­tion­ing of house­hold appli­ances (boil­ers, wash­ing machines, ket­tles), as well as water treat­ment aspects employed in var­i­ous indus­tries, ser­vice sec­tors, and fields.

Qualitative characteristics of water

Water is essen­tial not only for humans but also for var­i­ous dis­ease-caus­ing microor­gan­isms that can harm humans. To safe­ly use water, it is impor­tant to know that it is clean. Accu­rate infor­ma­tion about the qual­i­ty of water can only be deter­mined through lab­o­ra­to­ry tests. The qual­i­ty of drink­ing water needs to be reg­u­lar­ly checked as its chem­i­cal com­po­si­tion direct­ly affects our health. Analy­sis should be done peri­od­i­cal­ly, espe­cial­ly in cas­es where there are sig­nif­i­cant changes in the sen­so­ry prop­er­ties (taste, smell) of the liq­uid. The qual­i­ta­tive char­ac­ter­is­tics of ground­wa­ter are divid­ed into:
physic­o­chem­i­cal (alka­lin­i­ty, oxi­diz­abil­i­ty, salin­i­ty);
sen­so­ry (col­or, taste char­ac­ter­is­tics of the liq­uid);
micro­bi­o­log­i­cal (detec­tion of par­a­sites);
chem­i­cal (pres­ence of organ­ic and inor­gan­ic ele­ments such as met­als, pig­ments, petro­le­um prod­ucts, etc.);
radionu­clides.

Types of chemical analyses of groundwater

Field chem­i­cal analy­ses are per­formed dur­ing hydro­ge­o­log­i­cal inves­ti­ga­tions under field con­di­tions. Spe­cial so-called field lab­o­ra­to­ries are used for this pur­pose. Water field analy­sis includes deter­mi­na­tion of such macro-com­po­nents and phys­i­cal prop­er­ties as: pH, Cl‑, SO42‑, NO3‑, HCO3‑, CO32‑, Ca2+, Fe2+, Fe3+, CO2, H2S, SiO2, oxi­diz­abil­i­ty of dry residue. The fol­low­ing com­po­nents and indi­ca­tors are cal­cu­lat­ed: Na++K+, Mg2+, tem­po­rary hard­ness, min­er­al­iza­tion. The pur­pose of field analy­ses is to obtain a pre­lim­i­nary char­ac­ter­i­za­tion of the qual­i­ta­tive com­po­si­tion of water in the inves­ti­gat­ed area. They are per­formed in large quan­ti­ties and through­out the entire study area. This analy­sis is approx­i­mate and does not pro­vide accu­rate quan­ti­ta­tive char­ac­ter­is­tics of the pres­ence of var­i­ous macro- and micro-com­po­nents in ground­wa­ter.

In the abbre­vi­at­ed analy­sis, pH, Cl‑, SO42‑, NO3‑, HCO3‑, CO32‑, Mg2+, Fe2+, Fe3+, NH+, NO2, H2S, CO2, H2SiO3, oxi­diz­abil­i­ty of dry residue are deter­mined. The fol­low­ing com­po­nents and indi­ca­tors are cal­cu­lat­ed: Na++K+, total and tem­po­rary hard­ness, aggres­sive CO2. The abbre­vi­at­ed analy­sis is car­ried out using more accu­rate meth­ods in sta­tion­ary lab­o­ra­to­ries and allows for con­trol of the analy­sis of dry residue. Such analy­ses are per­formed dur­ing the search for ground­wa­ter to obtain a pre­lim­i­nary com­par­a­tive char­ac­ter­i­za­tion of sev­er­al aquifers.

Spe­cial analy­sis is most often per­formed accord­ing to the spe­cif­ic task of the tar­get­ed research. This type of chem­i­cal analy­sis allows for the deter­mi­na­tion of micro­com­po­nents or oth­er sub­stances that are not iden­ti­fied dur­ing a com­plete analy­sis. The results of deter­min­ing macro­com­po­nents in nat­ur­al waters are usu­al­ly expressed in weight, ion, equiv­a­lent, and per­cent-equiv­a­lent forms. The pri­ma­ry form of express­ing the results of water chem­i­cal analy­sis is the weight ion form. Oth­er forms of express­ing the chem­i­cal com­po­si­tion of water are obtained based on it.

Addi­tion­al­ly, for the pur­pose of assess­ing the san­i­tary qual­i­ty of drink­ing water, a bac­te­ri­o­log­i­cal analy­sis of ground­wa­ter is con­duct­ed. Ground­wa­ter, in gen­er­al, and fresh water, in par­tic­u­lar, con­tain a large num­ber of microor­gan­isms, rang­ing from a few hun­dred to sev­er­al mil­lion bac­te­ria per cm³. Path­o­gen­ic (dis­ease-caus­ing) bac­te­ria pen­e­trate ground­wa­ter from nat­ur­al dis­charges of humans and ani­mals. This intro­duces the agents of dis­eases such as dysen­tery, tularemia, infec­tious hepati­tis, etc., into the water. The bac­te­ri­o­log­i­cal com­po­si­tion of water is judged based on three indi­ca­tors: 1) by the num­ber of colonies that grow in the nutri­ent medi­um after adding 1 cm³ of the test­ed water (seed­ing); 2) by the colony-titer, which deter­mines the amount of water per bac­teri­um; 3) by the colony-index, i.e., by the num­ber of col­iforms in 1 liter of water. Water is con­sid­ered bet­ter if few­er colonies grow in 1 cm³ of water, the high­er the colony-titer, and the low­er the colony-index.

Author: Mel­ny­chenko Mari­na