If I have contaminated clothes from spilling seed, can I make the clothes pure again by taking them to the mikveh or a local body of water like a wellspring?
In Temple times, when the laws of ritual purity apply, the clothes would be immersed in the mikveh, or a stream of running water, and they would be pure with nightfall (Lev. 15:17).
Today, cleaning the clothes in the regular manner is sufficient for all halachic concerns. According to most opinions, there are no halachic issues even when the clothes are sullied (see Shulchan Aruch, Orach Chaim 76:4; Magen Avraham, and Maamar Mordechai 76:4; Chayei Adam 1:3 is stringent concerning stained clothing with regard to blessing and prayer, but the stringency would not apply after the garment has been washed).