For the most part, having a septic system in your home is little different than being hooked up to a municipal water supply. Water goes down the drain, and unless there is a problem, you don't really have to think about it again. However, the actions you take will affect how often those problems happen. When considering a major purchase that will affect your home's water usage, you should keep in mind how that purchase might effect your septic system's health.
Hot Tubs and Pools
Hot tubs and pools are a fantastic way to relax in the evening or on a weekend. Having your own hot tub means that you do not have to worry about how crowded the pool is when you want to use it. However, you need to be very careful when installing one of these items if you use a septic system to dispose of waste. The chlorine and other chemicals in the water are designed to kill bacteria and they will not make an exception for the beneficial bacteria living in your septic system. This does not mean you can't have a pool in your backyard, it just means that if you do, you need to be very careful when draining it. If you are dumping the water out into the yard, make sure it drains away from your septic system's drain field, or contract with a company to have the pool pumped out and the water taken away.
In the Kitchen
Your kitchen might be one of the most dangerous areas in your home for your septic system. Both your sink and your dishwasher are sources of potential problems for the tank. Once upon a time, it was a considered a bad idea to have a dishwasher if you had a septic system, but no more. Newer, more efficient units can be used in homes with septic systems, provided that you do not run them while washing clothes or showering. They still use quite a bit of water, and receiving large amounts of water from more than one source could cause the tank to overflow.
However, you should still avoid getting a garbage disposal for your sink. These devices exist only to grind up waste food, and make it tempting to throw things down the disposal that could go in the trash. The issue with this is that it only adds to the solid waste in your tank, requiring that you have it pumped more often. The better option is to use a drain filter when running the rinsing dishes, and emptying it into the trash, instead of down the drain.
Water softeners work by using salt to remove minerals from incoming water. They are most common with well water, but you could have one even if you are on a city supply. It really just depends on what mineral deposits are in the area, and what you are willing to tolerate, as far as water quality. Again, the issue is that water softeners dump large amounts of water, possibly hundreds of gallons, into your septic system all at once. As the tank starts to fill up in between septic tank pumpings, there is a limited amount of space in the tank before it starts dumping solid waste out into the drain field, resulting in system damage. Regularly pumping a hundred gallons or more into that tank is going to put a lot of strain on this system. Fortunately, since the softened water is clean, you can have the plumber use an alternate dumping area for this water, so that it does not put undo stress on your tank
When working with a septic system, water conservation is very important. While you do want to be able to go about your daily life, you also don't want to have to replace your septic system too early. Any purchase that has the potential to push a lot of water into your septic tank is one that you need to be very careful about.