Increased water consumption in foreign countries was stopped in the 90-ties by implementing the EU measures in order to prevent pollution of the environment by characteristic decrease in waste water discharge. The possibilities of extensive development are in many cases exhausted and the requirement of rational exploitation of water resources and adequate protection thereof is mostly applied.
Protection means creation of such conditions which may ensure their documented quantitative and qualitative regime. The most frequent and currently most effective way of protection are protection zones of water resources and their hydrologic river basins. The costs for establishment, maintenance, and operation of hygienic protection zones should also be considered.
The established regime in the protection zones of water resources, which is related to the requirements for the way of management of the land also results in the claims for indemnification of damage from limitation of the ownership rights of the land owners. The development in the need of drinking water is closely connected with the specific social and economic environment.
Significant decrease in water consumption in our country occurred after 1990, when during the period of 1990 to 1996, the value of water produced on national average decreased from 430 to 300 l per capita.day-1 and the specific water consumption for households from 190 to 140 l per capita.day-1.
From 1990 until 2001, the specific consumption of water for households in the Slovak Republic decreased, in respect of 1990, by 38 %. Due to changed economic conditions and increased prices for water, frequently below the limit of hygienic minimum 70 l per capita.day-1.
The average water consumption in households in 1999 – 2001 was:
- 1999 118.4 l per capita.day-1
- 2000 120.86 l per capita.day-1
- 2001 115 l per capita.day-1
Effect of Decreased Necessity of Water Decreased consumption of water not only in households, but also in the industry results in changes in the hydraulic conditions in the waterwork engineering system, as e.g. decreased velocity of water in pipelines and prolonged period of retaining. The prolonged period of retaining may be reflected in different qualitative and quantitative changes.
The following frequently occurs:
- Changes in the biologic stability of water,
- Changes in physical and chemical properties of water,
- More intensive corrosion and incrustation of metal materials in pipelines and equipment,
- Requirement to put more chlorine to the water in the system and thus possible changes in qualitative properties of water,
- Change in pressure conditions in the network.
Change in Biologic Stability of Water
Changes in the biologic stability are caused, in addition to temperature, pH of water, corrosion of material and other, also by the time of retaining water in the system. Change in the biologic stability may result in exceeding certain limit values applicable for quality of drinking water, and may cause also microbial corrosion of the material of pipelines, thus increasing the requirement for disinfection agents. In water reservoirs, mainly due to overdimensioning, where water may stay for a long time, microbiological contamination may occur also from the air.
Change in Physical and Chemical Properties of Water
The long time of retaining may result in a change in temperature, sensoric properties, reduction of oxygen, etc. in the transported water. Reduction of oxygen causes undesirable reactions in water, resulting in reduction of nitrates to nitrites up to ammonia, change in the the calcium-carbonate balance, change in pH, reduction of sulphates, etc.
Due to the long time of retaining and insufficient exchange of water in creation of the so-called dead corners, anaerobe conditions occur in accumulation rooms.
Corrosion and Incrustation of Materials
Change in physical and chemical properties of water, as well as the change in the biologic stability of water may result in increased creation of incrustations in pipelines and corrosion of pipes. Internal corrosion may be caused also by microbiological factors, microbial corrosion occurs, where the microorganisms react with the material of the pipelines and damage it.
Increased Requirements for Doses of Disinfection Agent and Occurrence of Precursors
Creation of a biofilm on the pipeline walls and objects leads to increased requirements for doses of a disinfection agent. Disinfection results in occurrence of undesirable products in water, as e.g. trihalometanes, chlorderivates of acetic acid, chlorphenols, etc. The additional chlorination along the path may result in worse quality of water.
Changes in Pressure Conditions in the Network
Decreased consumption of water and the related lower speed result in increased pressure conditions in the network and related increased loss of water. Roughness of pipelines and the related lower diameter result in increased pressure losses and thus higher energetic demands on the system.
Possible Solution in the Future
In proposing measures, we must be aware of the fact that dimensioning of a water main system is made for the period of 40 to 60 years ahead. It may be supposed that in future, the requirements for water supply may grow due to stimulation of industry or from any other reasons.
It may be assumed that the development in the need for drinking water in present and also in the future is affected mainly by the following:
- demographic development of the population and the standard of supply,
- development of the structure of the apartment fund,
- rationalizing measures in manufacture, transport, and water consumption,
- economic standard of development of regions and the price for water.
In many advanced European countries and elsewhere in the world, rain water is frequently used in households. This is due to the fact that almost one half of the water consumed in households need not meet the quality of drinking water. If we consider the fact that water from resources must be frequently treated with high costs, or transported to long distances, it increases the costs on the produced water, which is reflected in the price for water.
From the aspect of ever increasing requirements on quality of water and consumers´ requirements on water without „chlorine“, in the last period we often meet contributions dealing with use of membrane technologies in treatment of water. Ultrafiltration improves the hygienic quality of water, and by the membrane technology it was even possible to renew a microbiologically unsuitable water resource.
The firm WABAG made a facility for the output of 140 m3/hour, the largest membrane technology facility is used in the water treatment station in Méry – sur – Oise with the capacity of 140,000 m3/day and in Bavaria, 30 – 50 ultrafiltrating facilities are planned with the capacity 0.1 – 5 mio.m3/year.
Information and Contact:
Prof. Ing. Jozef Kris,PhD.
Doc.Ing. Oskar Cermak,PhD.
Doc.Ing. Marta Cermakova,PhD.
Slovak Technical University
Faculty of Civil Engineering,
Department of Medical Engineering,
Radlinskeho 11, 813 68 Bratislava 1,
Phone: 00421 2 5927 4111,
Telefax: 00421 2 5296 7027
