I have this medieval world with this big realm.
Its climate is dry and warm and the main issue is what to drink, how to do the hygiene, agriculture etc.
They have no access to seas nor mountains.
There are some rivers, but they're often dry and not so wide (therefore using pumps to fetch the water from these sources is not a lifesaving solution), but all the water they have is from the rivers - it is not enough though and people die a lot because of dehydration.
Simply water is rare in general. Digging wells is not a good solution either because the water is really deep in most of the country.
Rains also come very rarely, two or three times a year maybe (but when they do they are steady and heavy, they can last a week or even more).
- They could import water from distant places in tanks, but that is not so effective (especially when they need so much), probably very expensive and there is higher risk that the water will be tainted.
- They could somehow store the water from the rains, but I don't know how (also risk with contamination).
They have a really good king with a smart government and they want to help people and the realm. Also, the realm is quite rich, so they are able to invest a lot of money and energy in solving this. What possibilities do they have?