Compost toilet and off-grid water solutions

Been looking at this for my backup setup and got a few questions for the more experienced folks.

On the compost side, I'm trying to work out whether a proper commercial unit like a Separett or just a DIY bucket system makes sense. The commercial ones seem pricey but presumably handle the sawdust/urine separation better? Anyone running either setup long-term? How often are you actually emptying it and what's the smell situation really like during winter?

For water, I'm torn between rainwater harvesting with a proper tank system versus a borehole. Rainwater seems straightforward enough—guttering, filtration, storage—but I'm wondering about the filtration side. Are people just doing basic sediment filters or going full multi-stage? And does anyone bother with UV treatment or is that overkill for an off-grid setup where you're not on mains?

The reason I'm asking is I've got limited space and was thinking about a combined approach—rainwater for washing and toilet flushing, then something more robust for drinking water. But I'm not sure if that's overthinking it or actually sensible.

Also curious about winter considerations. I'm in the north, so tank freezing could be an issue. Are underground tanks the only real solution or have people had success with insulation?

Would be great to hear how others have tackled this, especially anyone who's had to troubleshoot problems after installation.

The Separett units are genuinely solid if you've got the space and budget—I've seen them perform reliably in permanent setups. That said, for a backup/emergency scenario, you might be overthinking it.

A simple DIY bucket system with sawdust and a urine diverter honestly does the job and costs next to nothing. The key is getting your carbon-to-nitrogen ratio right; too wet and you're asking for problems. I've run both approaches in my van conversion and the DIY version is far more flexible when you're not using it daily.

Main consideration: ventilation and odour control matter more than the unit itself. A basic 4" ducting setup with a small 12V fan makes an enormous difference. That's where budget is better spent.

What's your expected usage pattern? That'll determine whether commercial or DIY makes sense for your situation.

Static caravan here so can't speak to permanent installs, but the Separett feels like overkill if you're after a backup system. I went with a basic dry toilet and honestly, it's the smell management that'll haunt you more than the actual composting—invest in sawdust and a decent ventilation fan rather than a fancy unit.

For water, depends entirely on your rainfall and storage space. I've got 2,000L tanks fed from the roof and it covers maybe 70% of the year if I'm sensible. Supplement with bowsers during dry spells rather than plumbing in mains as a "backup"—defeats the purpose and costs a fortune.

What's your actual use case, @MaxFrost? One person in a shed versus a family in a cabin changes the maths completely. And if space is tight, a basic composting bucket beats a commercial unit every time—costs £50 instead of £3k and takes up less room than my battery rack.

@MaxFrost - Good question. I'd add that it depends partly on your usage patterns. If this is genuinely backup (say, a few weekends a year), a simple DIY urine-diverting seat over a 5-gallon bucket with sawdust is honestly hard to beat—costs you about £30 and takes up minimal space.

The Separett makes more sense if you're looking at regular use or longer periods off-grid. They're reliable, but you're paying for convenience and capacity rather than pure functionality.

One thing worth considering that doesn't always come up: ventilation. Whichever route you go, a proper vent pipe (even just a 100mm PVC pipe up through the roof with a flyscreen) makes an enormous difference to odours and speed of decomposition.

Also worth checking your local authority regs—some areas have specific requirements for permanent installations, though backup setups tend to be more flexible.

What's the actual usage pattern you're looking at? That'll probably make the decision clearer.

Depends what "backup" means to you, really. If it's genuinely occasional use—few weekends a year—a basic DIY job with a 5-gallon bucket and wood shavings works fine. Cheap, simple, no moving parts to fail.

But if you're talking weeks at a time or more regular use, that's where something like a Separett makes sense. The urine diversion is the game-changer—keeps everything drier and much less unpleasant to empty. You're also looking at way less smell and faster decomposition.

Space and budget are the real factors. Separett units aren't tiny and they're not cheap, but they're designed for exactly this job and they last years with minimal fuss. I've got a mate with one in a permanent setup and honestly doesn't think about it.

The middle ground loads of people overlook: look at the Nature's Head clones (Fogstar do decent ones). Pricier than a bucket but way less space than a Separett and still gives you that urine separation.

What's your actual usage pattern looking like?

The Separett's brilliant if you're generating proper volume and want minimal faffing about, but for genuine backup usage? You're paying for features you won't need.

I've got a Fogstar composting setup on my boat that's essentially a bucket with a seat frame and a good seal. Cost me about £150 total. Works perfectly for occasional use—the key is getting the carbon-to-nitrogen ratio right. Keep sawdust or coconut coir handy, layer after every use, job done.

Real talk though: what's your water situation like? Compost toilet is half the puzzle. If you're looking at emergency backup, you might want to sort rainwater capture or a borehole before splashing out on the toilet. A basic system with decent filtration (Victron filters are solid) will probably get you more comfort per quid spent.

How often are we talking—genuine emergencies only, or more regular use?