До тысячных долей и более gen.

[Maria-adel]

Высокая степень очистки: ДО ТЫСЯЧНЫХ ДОЛЕЙ И БОЛЕЕ. вариант: ...:to thousandths and more

[SirReal]

нет

to three decimal places

[Amor 71]

up to one-thousandths and less (not more)

[paderin]

http://www.naturalsolutions1.com/cq_ro_reverse_osmosis2.htm
as small as 1/1000 fractions and smaller