I think ponds/lakes are important for many reasons, including; Tradition.
Ponds are common in gardens in Thailand, as you can keep fish in there to eat (and frogs, insects, eels, tadpoles, and a whole bunch of other stuff all on the menu). Water on your property is also seen as good luck. Additionally I like to embrace and re-interpret the positive aspects of Thai culture wherever possible, so having a pond is a must. Environment.
Water is a cooling element in a garden, and although Chiang Mai has cool winters, as we have just experienced, the summers can be brutal. To sit in a sala next to a pond, sip on a beer.. ahhh Design.
A pond or standing water feature is a focal point to a garden, all things radiate out from it and is a very good starting point for a house plan, this is why I keep saying that I am making a garden with a house in it.Many plants only grow in or very near water, having a water feature will allow me to create a lushly planted oasis that I can plonk a house next to. Functionality.
If the water gets rationed (as it did in April), having a pond to fall back on as an alternative supply even if it's just to flush the loo or water the odd pot plant, it's better than now't!
I have looked at all sorts of ponds and lakes here in Thailand, some lined, some not, some look like industrial holding tanks, others look like they belong on a crazy golf putting course.
So here's my experimental pond design, I'm going for a controlled natural look: