Hello Lola,
My 18 month old loves taking baths, and she also drinks her bath water. She will suck on the wash cloth if she gets a hold of it before me. I at that point simply get another one until I am done washing her. Once I wash her I drain the tub and rinse her off. Once she is rinced off and clean, I refill the tub and let her play. She lays on her belly and tries to swim and then will put her face down to drink the water. Or fill her toys up and take a drink. It's fresh water and she is after all clean so I don't feel she is getting dirty water.
How this helps give you a peace of mind.
P.
About me. I am a 33 year old married mother.I work full time, have an 18 month little girl and just found our she is gonna be a big sister.