Finding out where you water comes will help you pinpoint the potential types of contamination that could happen. Knowing this information is very important in helping you take precautionary steps that that will protect the quality of your water and keep it safe. What type of water filtration system to use depends on the type of contamination that you are more likely to be subjected to.
The two main sources of water are ground water and surface water. Ground water come from rain, snow and hail soaks into the ground and collects in pores and spaces within rocks and in underground aquifers. Surface water comes from streams, rivers, lakes, and reservoir.
Between the two main sources of water, surface water is more susceptible to contamination. Chemicals from human activities such as fertilizers and insecticides in agriculture and wastes from manufacturing that are not disposed properly often gets carried by water runoff during rain or snow for hundreds of kilometers into different bodies of water such as rivers and lakes. There are also rotting organic matters such as leaves and remains of dead animals that can cause microbial growth in surface water.
Ground water is protected from certain contaminants due to the soil layers filtering larger contaminant particles. However, this doesn't necessarily mean that ground water is safer. There are naturally-occurring contaminants underground that poses health risks such as radon gas deposits and heavy metals.