Mvua zinaponyesha mahali mbalimbali maji yake mengine hunywea chini ya ardhi, mengine hutelemka kuelekea bondeni kama mito, maziwa na bahari lakini yaliyo mengi pia hutwama.
Maji yaliyotwama yakikaa muda mrefu hutengeneze uchafu, pengine matumizi yake huwa machache sana, na pengine kutotumika...