The best way to find out what water is really doing in your space is to go out and observe during and after a rainstorm. Were some areas shedding water as it fell? Did some areas seem to absorb every drop that landed? What areas are still dry? What areas are puddled, and what areas are wet with no sitting water? Was water moving somewhere unexpected? Now go back out 24 hours later. Are the puddles still there? Do you know where the water table is?
Where are the downspouts? How much water is coming down them? Is that water going somewhere useful, or is it flowing into a hardscape or the street?
Don’t forget about winter calculations. Are there areas of your space that freeze over with ice all winter until spring thaws them out? Where do you shovel your snow? Do you use de-icer? Are there areas that seem to dry out over the winter? Does ice skip the liquid phase and go straight to vapor (the technical term is sublimation)*? (It does that in the Rocky Mountain region and can actually cause damage and desiccation to plants.)
*Sublimation happens when a substance in a solid phase transitions directly to a gas phase, completely skipping the liquid phase. It is an endothermic reaction that takes energy (in the form of heat) from the surfaces touching it. Even though it happens at warmer temperatures, sublimation can cause more damage than melting at near freezing temperatures. While water going through the process of freezing RELEASES heat to surfaces, sublimation REMOVES heat from surfaces. Irrigating crops in freezing temps has been used as a way to limit the damage from a freeze. The freezing water actually protects leaves and buds from freezing to deeply.