The studies were made on the surface water and groundwater sources, the existing and future water production yields of the Riga city. The forecasts about water demand in Riga by year 2010 are estimated as 200 000 m**3 dE-1, with a variation coefficient of 1.13. Total water yield is estimated as 410 000 m**3 dE-1, with a storage coefficient of 2.05, which is considered as sufficient. It is proposed that in future 50% of drinking water for Riga will be abstracted from groundwater and 50% will be produced in the Daugava surface treatment plant.

The article deals with the regeneration process of water resources capacity of the wells in the Baltezers region using mechanical and chemical treatment. The methods of this treatment process are described in detail.

The work contains the description of the current technical conditions of the water resources of the Baltezers region and drinking water consumption in Riga during 2003-2010.

Estimating water quality of rivers, lakes and other water bodies, their contamination is being modelled according to the quantitative changes of pollution factors and their appearance conditions. Water contamination is being determined considering one or another value of contamination factors. The modelling of the impact of pollution factors on water quality becomes problematic when the values of the factors can be estimated only approximately or cannot be estimated at all. It is rather difficult to define qualitative estimation of water contamination factors in comparative terms (scanty impact, average impact, etc.) applying only quantitative mathematical methods. In this case the method of fuzzy logic may be of great help. Fuzzy logic enables us to formalise the comparisons of the ojects or phenomena under discussion as well as eliminates the contradictions between qualitative and quantitative methods. Those two methods supplement each other and can be easily applied together. The objective of the study was to estimate the possibilities of fuzzy logic application for the evaluation of stream water quality.

Stable isotope ratios of water (δ2H and δ18O) are important indicators which describe hydrological processes in the environment. These parameters allow to analyse structure, status, migration of pollutants and processes of the groundwater system. Groundwater from dug wells is widely used as a drinking water source highlighting the importance of investigation of water quality and its possible flows and sources. Despite available centralized water systems, there are still wide territories where dug wells are the main source of drinking water supply. Dug wells are recharged from shallow groundwaters which makes them more vulnerable to anthropogenic contamination. Therefore, quality monitoring and estimation of anthropogenic influences are of importance. Quality requirements of drinking water do not provide measurements of stable isotope ratios in drinking water, but the combination of those elements can be valuable for the characterization of impacts on groundwater quality. The aim of this study was to survey 64 dug wells in Eastern Latvia and analyse water quality together with measurements of stable isotope ratios. Measurements were performed twice, i.e., autumn and spring to track water sources in wells and describe the extent of possible impacts. This approach can indicate the magnitude of local factor impacts on drinking water quality. Surveyed wells provide high differences in analysed parameters, for example, nitrate concentrations in autumn varies from 0.44 to 108.26 mg LE−1. Also, other detected parameters are variable; therefore, tracking water flow with stable isotope values gives better insight into the water quality of the studied region.