In recreational vehicle you have limited source of fresh water as well as space for grey and black water (septic). One thing that uses quite much of fresh water and produces black water (septic) is toilet. At home one flush is about 8 liters here in Europe and about 12 liters in US.

A waterless toilet would be the ideal for RV use. There are several options for this path. Composting toilet, separating toilet (liquid/solids), burning toilet (gas/electric) or freezing toilet. 

Composting toilet is the simpliest, but there a some disadvantages. Smells, possible insects,...

Separating toilet is similar to composting toilet but urine is let to septic tank. Not ideal.

Burning toilet is expensive. And it uses quite much of electricity and /or gas. It need both in comming and out going ventilation pipes. And paper bags for every time youuse it. Not ideal.

I choose freezing toilet for my RV. It looks normal toilet seat outside. Inside there is a bucket with plastic bag. The toilet seat freezes the liquids and solids so that they dont smell. No water and no septic is needed so it saves both. And it uses only 300 W per day electricity. If power is lost nothing happens to it as it is air tight and it can also handle freezing environment itself if the RV happens to froze up.