Water for home patients
Saving/re-using reverse osmosis reject water at home.
Reverse osmosis (RO) reject water can be re-used at home, just as it can be in facilities.
Re-use options should be discussed with and offered to all/any home haemodialysis patient, though feasibility and effectiveness will vary according to the system used, and each individual home-set up.
In the US, where the NxStage system is the most frequently used home HD dialysis system, an RO is not required. The NxStage PureFlow™ either generates the dialysate on-line, or pre-prepared bagged dialysate is used – especially to support the NxStage travel mode. Neither generates RO reject water.
In Australia, New Zealand, Canada and much of Europe, home HD is more commonly provided by conventional single-pass dialysis systems. As these systems are similar to those used in facility-based care, each requires its own ‘personal’ mini-RO.
NB: The remainder of this ‘water section’ for home HD thus applies only to conventional dialysis systems, but when used at home.
For conventional single-pass dialysis systems used at home, some simple plumbing steps (see Figure 1) – with a one-off cost of ~AUD$ 2,500 – can save significant amounts of safe, effectively ‘potable’ waste water, for use throughout the home. This system has been previously described by Agar et al. and is depicted in Figure 1.
Figure 1: Recycling reverse osmosis RW at home
Some home water re-use options might include:
- Pipe-and-tank systems for garden maintenance.
- Store-then-drawn systems for:
- Laundry use.
- Toilet flushing.
- Dishwasher use (ensure an added softener).
- Animal/stock watering.
- Goodwill, over-the-back-fence, sharing for neighbour use.
- These re-use options are cheap to install and are much appreciated by patients.
- They help defray the utility costs of home care.
- They also allow patients to take ownership of, and pride in, the part they can play in making dialysis ‘green’.
- Regarding neighbour-sharing, reassurance may be required to confirm the quality of shared water but, once it is understood that reject water is ‘pre-patient water’ and not ‘used effluent dialysate’, fear is commonly allayed.
NB: While outmoded regulation still prevents a recommendation that the RO reject water is fit for human consumption, it does meet all EPA and WHO standards for potable (drinkable) water for human use. Remember, this is NOT effluent dialysate!
RW re-cycling through the RO – ‘continuous looping’
Another re-use option is to re-cycle the RO RW back through the reverse osmosis system in a continuous loop. It is a useful option to consider in areas where access to a reliable municipal water supply is limited, there is a reliance on rainwater, or the home lies within an arid or drought affected area.
This system comprises:
- A holding tank
- A larger storage tank
- A reversible pump
- A conductivity probe at the RO.
It permits RO reject water to be ‘continuously looped’ and to be re-used in the dialysis process.
After mains water priming, a recycle switch directs RO reject water away from drain and into ‘recycle mode’,
‘Recycle mode’ directs the reject water to the storage tank, then back to the RO system for re-use in the dialysis process.
A reversible pump drives the system and allows the storage tank to be back-filled (diluted) by mains water if a conductivity probe, located in the RO, detects a rising (unacceptable) conductivity reading in the recycling reject water and triggers an alarm.
Once the storage tank is satisfactorily diluted, recycling can recommence.
Figure 2: Diagram of recycled reject water system for use in haemodialysis
While the additional set-up costs are contentious, similar systems have proven to be relatively inexpensive. Local cost/benefit analyses should be performed.
Be aware that water quality needs to be assured, and disinfection processes will need to be maintained to ensure that the water delivered from the tanks remains within guidelines for water used for the dialysis process.
A note regarding septic tanks
When thinking about the disposal of dialysis effluent, there is one very important consideration – both for haemodialysis and peritoneal dialysis patients.
Dialysis effluent should not be drained into a septic tank for two reasons:
- The volume of water that haemodialysis uses will quickly fill a septic tank requiring more frequent pumping and drainage.
- The saline content (both HD and PD) of the effluent dialysate can change the microbiological pH and/or the milieu of the septic slurry, causing blockage and overflow.
- The high glucose content of the PD effluent can also promote the formation of a co-polymer … a little like thick egg white … that coats the surface of the septic and can block the lateral distributors.
It is therefore not recommended to drain dialysis effluent to a septic system if the household relies on a septic tank to break down household and toilet wastes. True, some more recent septic systems can handle the extra salt, but many cannot – especially the cheaper ones commonly used in individual homes.
Alternative methods for dialysis effluent disposal – such as rock pits and/or leach-fields – should be considered.
Read Home Dialysis Central’s KidneyViews blog for more details on this issue.