Do not allow the crawl space under a structure to remain flooded. There should not be any standing water there. The moisture will result in wood rot, corrosion, mold, and other undesirable effects.
As is the case with the majority of flooded crawl spaces, the most proximate cause is usually a construction defect. In my 30 years of investigations, every flooded crawl space I have seen was caused by construction defects. An investigation may reveal the person or entity who is responsible for your flooded crawl space. That is the person or entity who should pay for corrections.
Where could the water be coming from?
Try This:
Run some water into the showers and flush the toilets. Listen closely for the sound of running of dripping water. If the source of water is not immediately apparent, try using sewer tracing dyes which are non-toxic, bio-degradable, and harmless to wildlife. You might put red color in your roof drainage system, and fluorescent green next to the foundation outside of the structure. Photograph the act of placing the dye. Add some water to each location. Drainage from your roof should never get under your structure. Water which soaks into the ground outside your structure should never flood the crawlspace. Wait a few hours and see if the water under the structure changes color. Check it again several times over the next few days. Before and after photos of the flooding will help to provide proof. Always take more photos than you think you will need. For extra emphasis, place white plastic below the water level so the color of the water shows up better in the photos.