Water has the power to move mountains or shape the terrain. Just take the Grand Canyon as an example if you doubt this, cut deep through soil and rock over time by nothing more than a flowing river.
Water can have a more immediate effect on things that float or absorb water, sometimes taking a while to dry out sufficiently enough to avoid the heat and air necessary to create the perfect environment for microbes, whether mold, mildew, fungus of bacteria to grow and multiply. Playground sand and wood products can easily wash out with enough water flow, and whatever might be left is not really suitable for providing the capabilities it was installed to provide. We've seen some communities keep installing their landscaping mulch as frequently as every 6 weeks, when it washes out from rain or run-off, or blows away in high winds. This is not acceptable for locations where it is intended to last much longer, and it's what happens with wood mulch.
Water can quite literally destroy a playground and make it unusable until it is fixed, incurring significant expense that many playground owner / operators cannot afford to handle, typically including: removal of the safety surfacing, installation of a suitable drainage system (if none existed or it suffered damage beyond repair), sometimes removal of the play equipment itself (if the footing anchors are compromised, etc.), installing everything that had to be removed, plus purchasing to replace whatever was discarded due to water damage. As a result, many playgrounds languish within impoverished areas without the financial resources & kids playing on these unsafe playgrounds end up with serious injuries, or worse.
Planning for proper drainage is always important before selecting any form of surfacing, because even rubber mulch isn't good under water, because it wouldn't be a surface! There are ways to plan properly with such drainage options as water vaults, without the need and expense of French drains, box drains, and all that's involved. We've created a simple and easy to understand cutaway drawing that shows how to implement this, just drop us a note through our Contact page form. Typically one water vault of 1 cubic yard in volume for every 250 to 300 square feet of area is sufficient. However, knowing and adjusting for your specific soil circumstances is important.