Speak to Doug at daqua.co.uk.
His r/os are built with superior components, unlike the cheap eBay ones.
A cheap r/o can turn out to be more expensive in the long run. Cheap Chinese membranes aren't as efficient as USA manufactured ones are so your initial saving are negated by the extra cost of resin to polish the pure off to zero.
Cheap r/os are ok for coffee machines, drinking water and aquatics but not window cleaning as we demand water filtered to much higher standards.