I think this is now an important question. Should we go for VIP latrines (single-pit or alternating twin-pit version) or for UD-VIV latrines? [Just in case anyone doesn’t know these acronyms: VIP = ventilated improved pit, UD-VIV = urine-diverting ventilated improved vault − these are always alternating twin-vault systems, see blog of 16 January; info. on VIPs here and very well illustrated info. on UD-VIVs here.]
The problem with VIP latrines is that desludging is in practice rather difficult − not technically (there’s the excellent Vacutug, for instance), not organizationally (eThekwini Water, for example, has an on-going VIP latrine emptying programme − but eThekwini Water may not be typical: it’s a highly organized, well-staffed, and financially strong institution), but rather because local governments generally don’t offer a pit-emptying service and private operators can be expensive − so pits are often not emptied or at best only partially emptied. It shouldn’t really be a problem, but in practice it’s a major one.
It’s even a problem in some rural areas where there’s space to dig a new pit after 10 years or so. In South Africa, for example, tens of thousands of rural households were given a VIP latrine by the government (as part of the post-1992 social reconstruction of the country), and many householders think it’s therefore the government’s responsibility to desludge them, but the government doesn’t agree! (South Africa has very few eThekwini Waters.)
With the UD-VIV latrine things are very different. The small above-ground vaults can easily be emptied by the householder using a long-handled shovel, and the material removed simply buried on-site. This process takes no more than 30−40 minutes a year and costs nothing.
Of course, the eThekwini-style UD-VIV is not perfect − well, it’s almost perfect in eThekwini. But in other parts of the developing world (even in South Africa, outside of the four big cities) it’s less than perfect. For a start the cost of the eThekwini UD-VIV in 2003 was ZAR 2900 (then equivalent to USD 370 / EUR 230) + VAT (details here − but why is VAT charged on a latrine? Surely it should be either exempt or zero-rated). Of course, in eThekwini cost is irrelevant to the householders as they get their UD-VIVs free as they’re paid for by eThekwini Water and the government. But this is not a model that can be used elsewhere as in general governments can’t afford this level of subsidy.
The technical specification of the eThekwini UD-VIVs is pretty high (details, including a drawing, here; note that in this document UD-VIVs are called VIDPs with urine diversion − VIDP = ventilated improved double pit) − possibly too high. There would certainly seem to be the opportunity to reduce costs by adopting a lower spec. for, for example, the superstructure (which could be built by the householders − after all, in most rural areas of the developing world people build their own houses).
Is a separate urinal necessary? Could be that men and boys don’t aim properly and their urine enters the faeces-only compartment ? But males do have a high degree of ‘directionality’ and they should be encouraged to use it − a role for hygiene education here!
So, while I think on balance that UD-VIVs are ‘better’ than VIPs, there is some developmental work to be done on them to make them more widely applicable in the developing world − but this really shouldn’t be difficult at all.
Then there’s the added bonus of UD-VIVs: they can easily be converted to ‘proper’ EcoSan systems. Personally I think it’s better for most communities to operate UD-VIVs just as latrines for something like 2−3 years, after which they can be shown how they can be operated in EcoSan mode and, if they like that, then fine. It’s much better, at least in my opinion, to get communities to use latrines properly before exhorting them to “close the loop on sanitation” and delay the impending global phosphorus crisis by recycling their excreted nutrients.