The crawlspace can be a hotbed of mold. Sometimes there are hidden problems such as leaky pipes–long slow unnoticeable drips into the crawlspace that have been feeding mold colonies for decades. It’s best to clean it up since (older houses especially) share air between the living area and the crawlspace, but it’s not an emergency unless you have medical issues (asthma, other allergic, immune or respiratory issues.) If you suspect mold is there, you should do something about it, for your health, for your peace of mind.
Have a professional come in and check for mold because a professional will be prepared for whatever else is in the crawlspace, from human debris like glass to feral animals to rats, mice and pathogens. And just because there is water does not absolutely mean there will be mold. Much less likely in, say, Arizona desert than Louisiana bayou.
If you’re in California, you might want to give us a call and see about getting an assessment from Byebyemold.