Simple Finite Water Control

If an area is connected to an infinite water biome for example by a long water channel, this area is also valid to form infinite water. This will fix the water not beeing infinite at river / beach borders to finite water biomes. 

For example: it can not make water sources in plains biome. but if you dig a channel to a river biome and fill it with water, this area is now valid to form infinite water sources.