Friday, April 11, 2008

Digression: composting toilets

Will asked about composting toilets. Composting toilets are something I've been interested in for a long time, and that we've looked into a bit at DM. The executive summary is that when they are the only thing that will work, they're an attractive solution. They are a good alternative in a situation where you can't put in a septic system. They may also work better in situations where you have very a very tight water budget.

But if you have a choice of going with septic, you're probably going to prefer it. You don't save much money over a septic system by going with composting toilets, unless you are in the sub-1000-gallon range on your septic system and thus are overpaying heavily (because you can't really buy a smaller tank).

The really nice composting toilets are quite attractive, but the maintenance varies from a really lot to kind of a lot, and installation is a real problem. The waste has to wind up in the composter, which means that you either have to carry it there, or you have to have the composter under the toilet.

The composter is not small, so if you put it under the toilet, either you have to raise the toilet up on a throne, or you have to dig a cellar to put it in. Either way, you need to be able to get at it for maintenance, so that adds cost. And the ones that turn the waste automatically aren't cheap. So you don't wind up saving money over a septic system - multiply the cost of the composter and the installation by three in the case of our septic system, and you have a budget of $1300 per toilet. Good composting toilets, counting installation, cost more than that. So septic is cheaper for us.

You can do a really cheap composting install where you just have a litter box under the toilet that catches the waste, and then you carry the waste out to an outside composting system. But that's a big pain, and you probably don't want to do that if you don't have to. In a situation where you can't put in septic, or don't want to dig in a throne, this is a viable alternative, but it's not something that's going to catch on like wildfire - you have to have a bit of tapas to be able to deal with it.

On top of that, you have to do something with the waste water from your sink, because it's considered black water, not grey water. There are ways of dealing with it, but they involve variances that will be hard to get during the permitting process. If you have the time to prepare and make a serious case with the health department, it may be worth trying, but if that sounds like more work than you're willing to do, it's probably best to avoid it.

In our case, our perc test was a smashing success, and we have ample water, and a willingness to innovate with rainwater catchment and grey water, so we just don't feel like the compromises and cost of a composting system are the right choice. But we may well consider a composting solution when we set up our retreat cabin.