How often should I change my goldfish’s water? Is it okay to dispose of all of the old water and start fresh?

Water, especially clean and pure water is something that most of us probably take for granted. In the good old days of the distant past, most people could just drink tap water without any worries of any contamination. Nowadays, it is a completely different story. Having a good water filter for your home and for your drinking water is essential, unless, of course, you buy bottled water for all of your drinking water needs.
There is plenty to be concerned about when it comes to drinking water and the contaminants found in most tap water.
There is bacteria, strains of antibiotics, fluoride, chlorine, lead and other heavy metals and sometimes benzine and other harmful materials.
When looking at various makes and models of under the counter and counter top water filters, check to see exactly what they do and do not eliminate. Some remove only the heavy metals but do not remove other toxins that require a more sophisticated method of filtration, such as reverse osmosis.
Out of all of the water filters, there are only certain ones made for home use that actually remove all of the pathogens and chemicals such as fluoride and arsenic. Many of the other filters leave these toxins in the water even after it's been filtered.
It is very important to get the best possible water filter that will provide you with truly pure drinking water with the least amount of contamination and impurities possible.
Some refrigerators have water filters that are built right into the door. Some of these work well but most do not eliminate all of the chemicals from your water.
Personally, I prefer the Gary Null brand reverse osmosis water filter.
The Gary Null Water Filter is an advanced multimedia system. It combines the unparalleled bacteria and parasite removing performance of ceramic, with the chemical reducing ability of activated carbon, blended with a lead-eliminating media. Activated carbon removes more chlorine than any other material available on the market. For those individuals who want to eliminate fluoride from their water, the Gary Null Filter also contains a fluoride removing filter.
If you really want the best water filter for your money, this is the one to get and it's not really that expensive.
It sells for around $320.00 and the filters last about one year. The replacement cost for both filters is around $160.00 or so.
If you are looking for a cheaper way to drink purer water, you can surely afford a brita water filter, which does do quite a lot of good, but does not go as far as a more expensive and more effective water purification system.