Whether you are on municipal or well water, they both can introduce impurities into your hot tub that interfere with the proper chemical balance of your water. Having your water tested is one way to determine if source water impurities are too high but we highly recommend using a garden hose carbon block pre-filter no matter what kind of source water you use. A carbon block pre-filter can eliminate the minerals and metals from the water and all other impurities that are larger than .05 microns (The human eye can detect up to 40 microns). If you have a water softener system, it is important that you bypass this system if possible when filling your spa to avoid high calcium harness levels. Your garden hose that you use to fill the hot tub often has standing water that can introduce bacteria, mold and algae to your hot tub. Flushing the hose by running it for several minutes before attaching the pre-filter is recommended. You may need to clean your hose by capping the end of the hose with the nozzle and then adding ½ teaspoon of 99% Dichlor Chlorine granules to the other end. Attach the hose to the spigot and turn on the water. Let sit for 5 minutes then flush with water. The initial water will have concentrated chlorine so please dispose of it responsibly. You can also purchase an anti-microbial hose found at most major home improvement centers that is designed to inhibit bacterial growth and are great for warmer climates.