If we had cement, we could make concrete tanks both for water storage and septic systems.  Periodically you empty out the septic tank and use it for fertilizer.  That requires you separate human waste + food waste from chemicals you might use elsewhere.  This is why I have solar cement furnace high on my personal project list.  After water, concrete is the most-used man-made material worldwide, and cement is what holds concrete together.  It can also make stronger and longer lasting earth blocks.  Cement is just cooked rock.  Lime cements are cooked limestone, and with the addition of brick dust are closer to a portland cement.  Actual portland cement (the common type you buy at home improvement centers) is 5 parts limestone to 1 part shale fired to a high temperature, and then ground to a powder.  For water storage, you might want to have a lining to keep it clean and a way to treat it (filters, activated charcoal, etc), even if you are getting the water from a rainwater source.

Wood ash + water = lye.  Lye + fat = soap.  If for some reason you don't want to go to the local shop and just buy it, it's not that hard to make.  I tend to think in terms of biggest needs first.  For most people, shelter (house to live in, workshop), food, furnishings, and basic utilities (heating and A/C, water, sewer, electric) are what takes up the biggest share of personal needs.  Anything beyond that is nice to have, but I would worry about them, personally, after the basics are taken care of.  Go ahead and add something to the wiki about soap if you want, but I will be working on setting up a community workshop, a sawmill, and a cement furnace, since we need those before we can do much else.

water storage, monitoring and treatment are certainly important things for any community, i found a really good resource for information here - http://www.akvo.org/wiki/index.php/Main_Page - they've got information on a wide range of methods with plenty of links to other projects and resources, plus they seem to be devoted to continuing the work which is always good.