Referred to as the universal solvent, this is the prime agent in the cleaning process. However, though an excellent solvent, water alone is not a sufficiently effective cleanser to meet the standards most hotels require. Indeed, it does not even wet a surface properly, as its surface tension prevents it from spreading easily. For water to be effective in cleaning, it must be used in conjunction with other cleaning agents such as detergents, soaps and so on. From the perspective of cleaning, there are two types of water – hard water and soft water. Soft water is ideal for cleaning purposes and also to make up the proper dilutions of other cleaning agents.
Sources of water
Water is available in abundance in some parts of the country, but is scarce in others. Sources of water may be surface, sub-soil or deep soil.
Surface water- Obtained from streams, rivers and lakes, it may contain both organic and inorganic impurities in large amounts.
Sub-soil water- Coming from shallow wells and springs; it is not likely to be contaminated with suspended matter and organic impurities. However, some gases and mineral matter are generally dissolved in it.
Deep soil water- Deep soil water, pumped up from deep wells. has percolated through, much soil and rock to reach its resting depth. Therefore it has a very high content of minerals such as calcium, magnesium, iron, sulphur, phosphates and silica as well as dissolved gases such as nitrogen, carbon dioxide and oxygen. The mineral salts dissolved in this water results in its hardness and render it unsuitable for cleaning purpose.
These days most of the cities, towns and some villages have running water supplied by the public works department (PWD). This water is filtered and chlorinated before being piped.
Hard water and soft water:
Water that contains more than 60 ppm (parts per million) of calcium and/or magnesium is called hard water. When the mineral content is in the range of 61-120 ppm, the water is said to be more moderately hard and if it exceeds 180 ppm, the water is considered very hard. When the level of dissolved calcium and/or magnesium is below 60 ppm, it is said to be soft water. However, water from all sources contains varying amounts of calcium and magnesium, usually in the form of bicarbonates, sulphates and chlorides. It is their relative proportions that determine how ‘hard’ the water is and in what way.
Temporary hardness- This is caused by bicarbonates of calcium and magnesium being dissolved in water. Temporary hardness is so called because it can be removed by simply heating the water to a temperature above 72o C.
Permanent hardness- This is caused by sulphates and chlorides of calcium and magnesium dissolved in water. It cannot be removed by boiling and requires chemical treatment to render the water ‘soft’.
Effects of hard water:
Calcium and magnesium salts dissolved in water inhibit lather formation from soaps and detergents, so that much more detergent will have to be added to precipitate out the calcium and the magnesium before cleaning can occur. This process causes a lot of scum to be formed, which may further soil the surface, when hard water is used for laundering; for instance, it causes premature ageing of fabrics due to constant friction with the deposits from hard water. They also become coarse and uncomfortable to wear. Hard water also causes scale and fur to be deposited in boilers, pipes and various appliances. Iron and sulphur salts can cause discolouration. Sulphur also causes a rotten – egg odors. Dissolved phosphates, on the other hand, can actually enhance the cleaning power of some detergents.
Methods of softening water:
Water which has hardness greater than 50 ppm needs to be softened. Temporary hardness can be removed by boiling (or heating above 72oC). In the reaction that takes place at these temperatures, dissolved bicarbonates decompose with the liberation of carbon dioxide and the carbonates precipitate out as scum or fur these should be removed by filtration before using the water for cleaning.
Ca (HCO3)2 CaCO3 + CO2 + H2O
In the case of magnesium bicarbonates, the resultant carbonate further decomposes into magnesium hydroxide
Mg (HCO3)2 MgCO3 + CO2 + H2O
MgCO3 + H2O Mg (OH)2 + CO2
The most practical way of removing hardness, however, is to treat it chemically. This is done in one of the following ways:
Alkali method - The alkali calcium hydroxide is used to remove the hardness from water in this method.
Lime soda method – In this method, sodium carbonate and calcium hydroxide are both used to remove the hardness.
Addition of sequestering/chelating agents – Sequestering agents are organic or inorganic compounds that react with metallic ions and form a complex. These metallic ions will still be present in the water, but will be unable to react with soaps or detergents as they are held in the complex formation. Thus the water is rendered soft. The most commonly used sequestering agents are EDTA (ethyl diamine tetra acetic acid), NTA (nitrolo triacetic acid) and sodium hexametaphosphate.
Ion exchange method or zeolite process – Zeolites are hydrated silicates of sodium and aluminium. Hard water is made to percolate through the zeolite. In the chemical ion exchange reaction that takes place, any hardness is almost totally removed. Ion exchange units are available as attachments that can be fitted into the plumbing system at the point where the water supply enters the hotel.
Organic Base Exchange method - Organic base exchangers are synthetic resins containing the sulphonic and carboxylic acid groups. When hard water is passed through these resins, The acids react with the calcium and the magnesium salts to produce products which are non reactive. When the last two methods are used in succession, they yield very soft, pure.
MANWAL